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Chronograph tips

# Chronograph tips

by Tom Gaylord
Writing as B.B. Pelletier

This report covers:

• How it works
• The evolution of the personal chronograph
• The advent of the skyscreen
• Fly in the ointment
• Screen placement problem one
• Screen placement problem two
• Shooting perpendicular to the skyscreens
• Lighting
• Odd chrony info
• Summary

Reader Buldawg asked for this report, but several other readers chimed in and seconded his request. I have written about this before, but we have so many new readers that it is probably time to do it again. There are several definitions for the word chronograph, including a very accurate wristwatch, but the chronograph I am talking about today is one that measures the velocity of a projectile. We are interested in pellets, mostly, but the chronograph was created to measure the velocity of bullets.

### How it works

A chronograph works by counting time between two events. In today’s discussion those events are the passing of a projectile through two electronic screens. The first one starts the clock and the second one stops it. So we call these screens the start and stop screens. The counter parses time into very small intervals. In the case of my Oehler 35P chronograph the counter divides each second into 4 million units. So time between the start and stop screen is measured in 4-millionths of a second.

There is no difference between this and a pneumatic hose laid across a road to count traffic, or across a gas station to ring a bell when someone drives in. When Bill Gates invented that device (for the roads, not the gas stations), he told buyers it could count traffic and it could also measure the speed of vehicles, if the distance between the first and second hoses was precisely known and remained constant. Radar guns were more accurate, though, and didn’t have the problem of the hoses moving, so Gate’s invention was relegated to counting axles.

### The evolution of the personal chronograph

Before the 1960s, ballistic chronographs were laboratory instruments manned by a staff of trained personnel. Chronographs became affordable to private individuals in the early 1960s. Back then the technology was crystal clocks that pulsed at speeds in the 10-100khHz range. Their results were displayed on nixie tubes that had to be interpreted through tables. Direct velocities were not given.

The screens used at this time were paper with wires running through them. The wires were attached to connectors on both side of the screens. When a bullet passed through the screen it broke several of the wires, changing the conductivity through the screen. This was sensed by the circuitry in the chronograph and served to turn the “clock” either on or off. There was a start screen that turned the clock on and a stop screen that turned it off. It was a brute-force approach to the problem, though, and suffered from imprecise results. If you went through a hole left by a previous bullet, there was no reaction. And after awhile, the screens were shot up and had to be replaced.

### The advent of the skyscreen

It was Oehler who first gave us the “skyscreen” — a screen that used a photo optical sensor to detect the passage of the bullet/pellet by sensing the reduction in light (the shadow) as the bullet passed over the narrow aperture of the screen. I am going to call this aperture the optical curtain. You are already used to these sensors being used to automatically open doors whenever someone approaches, so this is just a different application of the same technology.

The skyscreen changed everything for shooters. Not only did it eliminate the need to buy replacement screens, it also did not get shot up in normal use. A chronograph with skyscreens can function for hundreds of shots without intervention. Suddenly the \$300 that was paid for a chronograph (1970s money, so \$1,000 today) didn’t seem like such a burden!

The skyscreens have to be exactly spaced for the chronograph to work correctly.

### Fly in the ointment

Ah, but even skyscreens aren’t perfect — and therein lies the gist of this report. It is possible to get spurious readings when using skyscreens, and the problem is — most people will never know it. Today’s chronograph shows a velocity in both feet per second and meters per second on a large digital screen. The problem with that is whenever most people see a number on an instrument display — they believe it. And most of the time that number is wrong — just as the speedometer in your car displays the wrong speed most of the time. To get the right speed (in either the car or on the chrono) everything has to be rigidly controlled.

### Screen placement problem one

Screen placement is of paramount importance. Think of the skyscreen aperture as a thin optical curtain that extends straight up from the screen. When the pellet pass over (through) this curtain, it lowers the light hitting the photo receptor in the screen. That triggers the clock to either start or stop.

If one screen is not parallel to the other, the readings will be incorrect.

If one of the skyscreens is not parallel to the other screen, the space between the thin curtains is different than the computer in the device expects it to be. A difference of one-eighth-inch (3.175mm) spacing will give a result that is a serious percentage different than the correct number, depending on the clock speed.

Let me make it simple You will see the number 850.5 f.p.s. on the display, when the true velocity is 829.7 f.p.s. You will dutifully record the number you see and you will be a little more than 3 percent off the actual velocity — all because one of your skyscreens isn’t pointing where it should. Incidentally, in this case, the amount you are off will vary, depending on how high or low the muzzle is when you shoot through the screens. because the screens aren’t parallel, the separation varies with the distance above the sensors.

### Screen placement problem two

The screens are supposed to be a specific distance apart. Let’s say that distance is 12 inches. But what if one of them is 1/8-inch closer than it should be to the other screen? Again, you will get the wrong number. This time the screens are parallel, but they are spaced incorrectly. This time the amount of error won’t change as the pellet rises or falls against the sensors — just as long as the pellet’s flight through the screens is perpendicular to the sensors! And there lies the next, and by far the most common, chronograph problem!

### Shooting perpendicular to the skyscreens

When you shoot you have to hold the barrel of the airgun perpendicular to the optical curtains extending up from the skyscreens. If you don’t, the pellet will take longer to trip the stop screen, which will lower the recorded velocity. This is the most common fault shooters make when using chronographs. They get careless because the chronograph seems so forgiving, but what they are really doing is helping it to lie to them more convincingly. The displayed number looks so official!

If the bore is not perpendicular to both skyscreens, the reading with be incorrect.

### Lighting

Everyone soon discovers that the lighting has to be constant. If it pulses like fluorescents do, the optical screens will trip and the chronograph display will go haywire. But what people don’t appreciate is that the skyscreens also need even constant light to function correctly. A cloudy day is perfect, as long as the clouds aren’t moving around. If they are the chronograph will go crazy.

Direct sunlight will kill the skyscreens. It’s like looking directly at the sun with your own eyes. That is why the translucent shades are provided with the instrument. Most of the time they aren’t needed, but when they are you’d better have them!

In my office I use a white ceiling and I bounce a 500-watt photo light off it. It works perfectly. Are my numbers correct? Who knows? The best I can tell is they are consistent — reading to reading — because I always set up in the same way. Those numbers look impressive when you read them and I never get called on them, but I would not bet a lot of money that they are 100 percent correct.

### Odd chrony info

The faster the clock speed the more precise the number you get. Screen spacing is still important, but if it is exact, the numbers are pretty close to reality.

Screen spacing is important. My Oehler separates the start/stop screens by 24 inches, which is give more precision than my Shooting Chrony Alpha Master that separates the screen by 12 inches. If the clock speed were the same, the larger screen separation would triumph. I used to own a British chrono that attached to the muzzle of the gun. It had about 2 inches separation between the screens. It still gave me a number, but how precise could it be?

There are chronographs that use infrared light and there are chronographs that use induction (the passage of a mass that produces an electromotive force close to a sensor). I can’t comment on the induction chronos because I have never tested one. I’m sure they give you numbers, but how accurate they are is for someone else to say. The IR chronos work fine, but watch out for the sun if you use them! The sun through a skylight can cause a problem.

### Summary

These are the basics of using a chronograph. The most important thing to remember is that all chronographs will give you a number. The question is — do you trust it?

Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.
Categories Air Guns

### 114 thoughts on “Chronograph tips”

1. Looks to me the easiest thing to do wrong is not
holding the gun barrel parallel to the chrony eyes.

And next would be on the Chrony brand chronograph’s is not having the chronograph opened all the way so the eyes are both facing straight up.

And if you was to do both at the same time you could get a real slow reading.

So maybe the chronographs that don’t fold are the more precise chronographs. Well as long as you get barrel parallelism correct when you shoot.

• GF1,

I should have emphasized it more but even Shooting Chronys are not assembled exactly. They are close, but the screen separation can be off. All chronos with moveable screens have this problem as well.

B.B.

• BB
Never gave that a thought. Why I don’t know. But yep that would be another added variable.

• Maybe the chronograph should be mounted to a gun vise so that the gun, either pistol or rifle, when mounted is always oriented to shoot perpendicular to the optical curtains.

2. B.B. Thank you again for very simple but very good report! By simple I mean easy to understand! I Chronograph everything that will shoot through the two sky screens! I’ve purchased airguns that the seller says I chronograph the guns! There so and so fps! Like they are chronographed and that makes it good or great? Well the first thing that I do is chronograph with about every pellet or BB that I can test! Indoors/outdoors etc.! When the rebuilds and modders start messing with mother nature they must get a real thrill when they increase the f.p.s.? I use a chronograph as a guide and enjoy seeking out or finding out for myself what the fps actually is! Semper fi!

• J.Lee,

To answer your (?),……yes it is a thrill. One, it is nice to know the “health” of the gun for future comparison down the road. Two, it helps to discern “what did what” when doing a tune or mod.,…. learning.

It is my belief that things in general can always be improved upon. Cost control dictates that more often than not, less than optimal parts are used. That is part of the fun,….making something into all that it “could” have been. Yes, there is limits, but it’s fun finding out how far I can take it.

It may not be everyone’s “cup of tea” to modify their toys,…. but for those that do,……it is not a matter of (?),….but rather a matter of (!). Each to their own.

3. I had to look it up, Bill Gates and Paul Allen ran a small company called Traf-O-Data and sold a computer to the city of Seattle that could count city traffic.

“How it works” last word 2nd paragraph axels is probably axles.

“Screen placement problem two” 1st sentence should have a comma instead of a period I think and the next to the last sentence agains is against.

“Lighting” section 3rd sentence. Biut should be But

I just purchased a Chrony and learning how to use it. Would it be better to lay it flat on a table or should I mount it on a tripod?

• Siraniko,

Got them. Edith would be proud of you.

Thanks,

B.B.

• Siraniko,

To answer your question, I like to have mine mounted on a tripod with an adjustable head. This allows you to align your chrony parallel to your barrel much easier. If you shoot from the same bench, in the same place, at the same angle everytime you shoot then placing your chrony on a table will work for you. Since I change shooting locations frequently and sometimes need a chrony the tripod works best for me.

kevin

• Kevin
I’m sure Buldawg will chime in today. But he has his chrony mounted to a tripod.

But you still have to make sure if you have the folding type that it’s open all the way and the eyes are pointing up correctly.

• So, as in all scientific endeavors consistency is the key for reliable measurements.

4. B.B.,

I can attest to the 500W light shown at the ceiling (works). You may remember that when I first got mine, same as yours, I was ready to shoot IT. Through some trial and error, and the purchase of a 500W Halogen, all is good.

After reading this, I went straight to mine, poked in the steel rods and broke out the tape measure. (duplicating the vertical lines in your illustrations above). Right side, facing the front, 12″ at bottom and 11 15/16″ at top. Left side, 12″ at bottom and 11 3/4″ at top. The rods do have some slop, so I won’t give much credit to the test. Wrapping some tape around the rods to give a precise fit would be best and give the truest measurements.

Mine is permanently mounted on a tri-pod, but I will give this some more consideration the next time I have it out for testing.

Oh yea, one other tip for the readers,…..replace the steel rods with something that will break. If you hit one of the steel rods by accident with a pellet, the force may transfer down the rod to the plastic case holding the “eyes” and break the case. Since I do the indoor 500W version of testing, I do not use the rods. With the 880 arrow project testing though, the ol’ chrony will be heading outdoors for the first time.

Good article and one that I believe added to what you have previously written. Thanks, Chris

• Chris,

The rods are for holding the screens up. They have nothing to do with the reading. You can bend them all around if you want and they will not affect the reading unless you bend them into the flight path of the pellet and it ricochets off of it.

Those lines are the path of light entering the detectors.

• RR
Glad you said that because I was going to.

The eyes are what have to be positioned seeing straight up.

• RR,

I thought it was clear that I meant that the (vertical) lines in BB’s illustration represented the beam going up. I still believe this to be true and is a way to measure how the eyes are aimed,….(by using the rods that support the screens). An extension of the beam if you will, that will exaggerate the mounting of the eye housings. Stick the rods in and not unfold the chrony all the way It will be very obvious and goes directly to what BB pointed out.

• Chris USA
I used a example below about a metal ruler held to the side of the eyes housing. Then of course measuring across.

But the thing about using that might not be right either. Maybe the eye can have variables of how its mounted in the eyes housing.

We have photo eyes or sensors we use at work for different purposes. Like to see if a part is in place on a conveyor and such. Let me say this. The eye is not always seeing true to how it’s mounted in its housing or fixture. We have to shim the brackets or bend them to get the eye seeing correct.

The whole thing about all of this is there is all kinds of variables in the chronys construction and parts that can cause different readings. And probably even more so from one chrony to the next.

To be honest about it all. Is I want my chrony to give me a reading the day I’m using to compare to notes of other days of use.

I actually shot my chrony in the middle where it folds. Just nicked it. Didn’t even scratch the paint off. But also it was nowhere near the eyes. But here’s the important thing. I continued to chrony my guns that day. And my readings where exactly the same as before I shot the chrony. So there’s somethings that will affect the readings. But the main thing is collect data and document if you want to make sure you get results to compare too.

• GF1,

Good points. My idea of using the rods as an “extension” of the eye housings would do the same as your ruler. IF, the eyes (inside) are not mounted true to the housing’s (outside) dimensions, then yes, there is a problem. In fact, I would guess that is the problem between yours and Buldawg’s readings. One of you has a crooked mounted “eye” (within) the housing. That is something that can’t be seen and might not be able to be measured?

I do not take all this too serious. All I want is a reading and if I do (my part) on setting everything up true a straight, then I am happy with what I get and am confident in using the readings.

I bet someone here knows how to make those eyes “visible”, one way or the other.

5. One other tip,…I have taped a fiberglass driveway marker rod on top of the barrel. This allows you to have an extension of the barrel that goes (through) the chronograph. When used with a full rest and the rods in place, it will allow some measurements to be taken for reference. I do not use the rod on the barrel when testing,…only set up.

I do not do it anymore, but it is a good tip for anyone just getting started in chrony usage. Outa’ here. Chris

• Siranko,

A rod down the barrel would do the same, if you could find something that would work. TIG rod or braising rod comes to mind as well a wood dowel rod. It will get you “close enough” to avoid any major errors.

• Chris USA
You must not value the importance of the rifling in your barrel.

At the most I would use a wood dowel rod in my barrel but not no wire or anything hard that could damage the rifling.

• GF1,

While you are no doubt way above me on metal hardness and such, I find it hard to believe that any metal rod placed (gently) in an airgun barrel would do any harm. I do not plan on doing it, as I have no need to. The 880 and steel darts are another story. That is a 37\$ gun and was bought to play with. If all goes well, it (won’t) be the (inside) of the barrel I am concerned with anyways.

It was just an idea. Maybe not a good one? Wood dowels can be had down to 1/8″ and might be the best option.

Outa’ here,….Chris

• Chris USA
Wooden dowel rods or even a plastic rod maybe. Or of course cleaning rods and such.

But coat hangers and stuff like that is big no for me anyway.

The side of the wire might not be bad. But a sharp corner on the wire where you insert into the barrel to me is not good.

• GF1
Chris stated a fiberglass rod taped to the TOP of the barrel not a rod inside of it so he was not meaning to insert rod in bore.

BD

• BD
Here’s what I was talking about.

“Chris USA
March 1, 2016 at 6:09 pm
Siranko,

A rod down the barrel would do the same, if you could find something that would work. TIG rod or braising rod comes to mind as well a wood dowel rod. It will get you “close enough” to avoid any major errors.”

• GF1
Well yea that is a big no no for sure unless it a wooden dowel and then only if its to dislodge a stuck pellet. Agreed 100% to no hard objects in my barrels either and even cringe with a cleaning patch and only use them when accuracy is suffering.

I do like your trick of a couple drops of silicone oil in the barrel every 500 or so shots as it really seems to keep fouling at bay for extended periods.

BD

• BD
Yep the couple of silcone drops in the barrel where the pellet loads does work good.

But too much is not good also. I only do that if I see accuracy change and I know it ain’t from something else happening. And I may do the couple drops evry 1000 or more even of pellets fired. It just don’t need done often. And I never clean my air gun barrels at all. I just don’t poke noth’n down them but pellets and air. 🙂

• GF1
Yea only a couple drops for me as well and I may oil to often but I have not seen any negative results from a couple drop every 500 or so pellets at this point with my guns and definitely no negatives in my FT guns at all.

So just use sparingly is what I do. To me its easier than lubing pellets

BD

6. Probably the most important thing when using a chronograph is to be consistent.

How well is your chrony built? Were quality components used in it? When was it last calibrated? Are lighting conditions identical? Are all involved angles identical?

The secret to using a chrony is to not get too hung up on using a chrony. It is a great diagnostic tool, but it is easy to rely on it too much. When you are tuning an air rifle or pistol, it can be real handy. Once you have it tuned, put it away and shoot. After a few thousand shots you might want to pull it out and see how things are going, but unless you are an engineer, you don’t need to pull it out every shooting session.

Just go out and shoot.

And BB, get the P44.

7. B.B.

Do you know the clock speed, cycle rate, of the Shooting Chrony’s? I believe they are the most popular model of Chronograph on the market.
Other than faulty crony set-up and un level shooting angle, please talk about other ways to get false readings, i.e. muzzle blast.
Thanks,
-Y

• Yogi,

No, I don’t. I have asked them several times, but they decline to say. I think it’s safe to assume they are slower than Oehler, because Oehler is the industry leader and if they were faster they would advertise the fact.

B.B.

8. Thank you, Tom!

I’m a chimer on this question, and as usual, you provide the basic answers and the important questions.

I have used a Chrony, and it always seemed difficult to set up. Even when I had it “right”, it would give me errors. To me, it seemed very crudely designed. Then I bought a Caldwell “Ballistic Precision Chronograph”, and it seems a lot better generally. It has a cable, and software for an iPhone or Android phone. So, you can log data and get basic statistics shown on your phone, then send the log to your email. They claim to calibrate every unit to +/- 0.25% at the factory. Yet, much of your concern still applies. There are many online reviews of this unit (Chuckhawks has a good one).

Even with some expected errors and issues, the idea of being able to get a consistent velocity over a string of shots is so basic to airguns, that using a chronograph is vital to accuracy. It can be like using the Pelletgage, in that knowing whether your gun is shooting 750 fps or 800 fps is not as significant as whether it will hold consistency shot to shot. And finding out which pellet is the most consistent is also important.

I know there are readers who will fill in more about the concerns raised and how they use theirs,..

regards,
J

9. Excellent blog B.B.! Very well explained! I will send a link to a couple of friends who could appreciate this.

I added a couple of pieces of angle iron to the base of my Chrony and shimmed them (as best as I could) to get the curtains parallel. The angle irons straddle a 2×4 that mounts to my shooting rest to keep everything (reasonably) aligned and consistent when I am shooting strings for baselining and checking performance.

I have always wondered how “real” the numbers were but for my applications, with my setup, I am comfortable knowing that a delta in the displayed numbers is accurate enough to be valid.

Been using your “halogen off the ceiling” trick – works great!

Thanks B.B.!

Hank

• Hank the curtains? Or sun shades?

The eyes are what’s important to be looking straight up. Read what RidgeRunner wrote to Chris USA above.

• GF1

By “curtains” I am referring to the sensor’s field of view that the pellet passes through. I have always visualized it as “hanging” over the sensor – hence me calling it a curtain – sorry if I was not clear.

I am with RidgeRunner. I use my Chrony for getting base-line information that I will reference to later when I want to check a rifle or if I want to compare pellets. Not for regular shooting sessions.

For consistency, my Chrony is attached to a base that is attached to the shooting rest. All is fixed square and level and I can repeat the setup any time I want. The rifle to Chrony distance/angles stay relative so I can shoot at different targets and still get valid results because the alignment doesn’t change.

If my numbers say 950 fps, it doesn’t matter to me if the real velocity is 925 or 975 fps. The 950 is my baseline and if it changes then I know something is different.

I adjusted my HW100 to shoot JSB 8.44s at 950 (on MY chrony) and find that JSB 10.43s shoot 850ish… about 100 fps for the change in weight – a ball-park of 50 fps change per grain. Gives me a rough idea of what I can expect if I try other pellets.

I design and make wooden “self” bows – I consider a chrony to be a critical piece of equipment for anybody who is into tweaking for performance. Not really needed for the casual shooter, but still nice to have.

Just my nickel…

Hank

• Hank of course all the chrony is used as is a reference.

I have shot spring guns; well my Tx and the LGU just to name a few; outside over the chrony on different days in different temperatures and humidity. The guns have gotten different readings on different days. And they ain’t even pcp’s. See what happens with a pcp gun outside over the chrony on different days.

So as it goes the more you use them the more you will see different things. Just like shooting.

10. I use my Chrony every day for testing and have found that the actual numbers you get aren’t as useful as the variation you get. If the rifle is consistant with a low deviation in most cases the rifle will be accurate unless you have a barrel problem( and that should show up in the numbers you are getting). This is a place where alot of guys get really goofy also, no need to get the laser out to make sure the chrony is level and the barrel is level so it’s an exact 90 degree set up, just keep it consistant…there are those that will disagree with me but thats what I have found…velocity isn’t what you are looking for just a consistant velocity…
for the very best you need to contact the mfr. and find out the exact distance they have for the distance between the sensors, then use a micrometer to set the distance with your unit, then a 4000 lbs. plate that is perfactly level, then a mount for the rifle that will put the barrel perfectly level, weigh each and very pellet, size, etc…
oops may have given someone an idea here…guys the idea here is to have fun with the rifles and get them shooting where you can actually hit what you are shooting at…if you aren’t the worlds best shot don’t worry about it, just have fun…

• Mike,

I agree with everything you say, but GunFun1 and Buldawg were having a conversation about why one of them was getting different results than the other with the same guns. I was just trying to point out where the differences can come from.

B.B.

• BB
And I believe you did. And I just want to point out that having the barrel parallel to the eyes is very important. I also try to keep my barrel the same distance above the eyes every shot along with distance of the barrel away from the first eye.

Every way that the eyes are off or the barrel is placed can give false readings. And the more your off the slower the readings will be.

Now if all of those must do things are followed by two different people shooting the same gun with same pellets in different locations of the country with different chronys. Then that’s where the next question comes in.

What could cause the variation in readings? It sounds to me like possibly the slower reading chrony could have eye alignment problems. And then we keep thinking about air density. Not so much as more or less oxygen at different sea levels. Matter of fact we are both at pretty much the same sea level. But we thought maybe how thick the air is. If the air is more dense in my area and less dense in BD’s area or vise versa then we could get slower or faster readings then possibly.

11. yup, we could list all the different factors that can change the performance in a rifle but do we have the space and time? I have found that even the type of battery used will affect the chrony used, As usual air guns are a funny beast…give me a call Tom, have the Sentry from Xisico here for testing, know you are busy but…

• Mike,

I’ll call later this afternoon. Got to see the doc this am.

B.B.

• Mikeiniowa
Xisico sentry, is this a new model you are going to be or are selling now and if so, is it on your site yet or still in the prototype/testing stages so it cannot be revealed to the public yet.

Inquiring mind want to know.

BD

12. B.B.,

To me using a chronograph is always a frustrating experience, sometimes very frustrating, sometimes only slightly. This report has me thinking that I need to concentrate even more on my shooting technique than I already do as I try to get them to work. I will print this one out and reread it many times.

Even though we have many overcast days here in the Great Lakes states, I have had precious little luck using either of my chronies, a Shooting Chrony (very poor) and a ProChrono (somewhat poor) outdoors or indoors. Indoors I have no flurescent light in the room and experimenting with indirect, diffuse incandescent lighting of various brightness levels, I have purchased the factory lighting kits for both with fewer velocity figures than error messages.

Even though I have a chrony permanently set up in the basement, I usually bypass it in favor of a notebook I keep with data compiled from shooting CPLs at two feet into a phone directory.

Michael

• Michael
I use my chrony. But like you mentioned with the phone book. I have a peice of 2×4 that I shoot into when I make a change on a gun or try out different pellets. And a note. I do try to keep the barrel the same distance away from the wood and I make sure the barrel is perpendicular to the wood. I stick a small Allen wrench down in the hole and touch the pellet. I mark it with my thumb nail then take it out of the pellet hole and measure it with my 6″ machinist scale. You can actually get some pretty good readings that way.

13. Tom, thanks for this topic.

For example, at typical chronograph distances, has a shot column started to form and/or has the wad started to separate from the shot? If so, doesn’t that affect chronograph accuracy?

Tedd

• Tedd
I have chronyed a shot gun before.

Keep the sky screens or shades off. And the rods too. Hold the barrel of the gun about 12″ above the chrony and back from the front eye of the chrony about a foot and a half.

If you do that the shot blast shouldn’t do anything. Just like if you was to do a rimfire or center fire gun. And the wadding and shot will still be tightly packed together at that distance.

So you should by no means shoot your shotgun at the chrony at farther distances. The farther away the barrel is from the front eye when you shoot that could be a problem. The shot pattern will start opening up. Then you could shoot the chrony.

14. Good article with much of what I have been considering in the purchase of a modest chronograph (Shooting Chrony / Competition Electronics). I would probably go with the CE but the optional computer software (impressive looking) does not run on Windows 10.

With respect to pure accuracy, it is just like a motor vehicle gauge, how do we know it is accurate? We do not know if it is completely accurate. I guess about all I can hope for is consistency. I like the high wattage light reflecting off the ceiling onto the diffuser screens for consistent performance.

• CraigH
Just like a motor vehicle gauge. There can be variation. But like you said consistancy is the key factor.

• I live near Competition Electronics. I took one of their units in to check the calibration. Their method of testing was to put it in a fixture in line with an Oehler and shoot an airsoft pellet from a gun in the fixture through both. They read the same.
very nice people to work with. They will repair their units even if they’ve been shot for cost of parts. One stray pellet from a skeet load nailed it.
Also in testing firearms temperature can make a big difference.
Fido3030

• Fido3030,

It sounds as if you are in the calibration business. How do you check/what do you use, to see what the actual speed is? Is there anything that can done to adjust it if it has an off reading? Very interesting.

Thanks, Chris

• CHRIS USA
Hi Chris, Sorry, I just took it in for them to check. It was right on so they didn’t adjust anything. I don’t even know if there is anything to adjust or how to open the case without destroying it. Sorry. Fido

• Fido3030,

Thanks for the reply. If you find out any more info. on how they are tested, that would be interesting.

• CHRIS USA
Chris, I did a google search of “diy chronograph” and found a lot of stuff for pellets, airsoft and paintball. There are ones that look easy to build and plug into a laptop with downloadable software.
Hope this helps. Fido

15. HI B.B.
Thanks so much Sir for this timely article. I’m thinking of buying a Chrony & its so good to know the pro and cons of using them. God Bless you.
Errol

I am having a ball just playing with all my toys and thats what it’s about!

Bruce

• Bruce
They are actually pretty simple to set up. I use mine outside mostly in the sun and in the shade and never have any problems getting consistent readings.

One thing I can recommend is when outside in the direct sun light and the sun sheilds are used. I take and rotate the chrony around in a 360 degree circle so to speak so the shield’s throw a equal shadow over the eyes. That has totaly helped me be able to use the chrony out in the direct sun.

• A technique I saw online was to place a piece of poster board or flexible cardboard between the screen tops to help block ambient light from the sensors if any odd problems are being experienced. When I get one I am going to also extend the poster board a bit beyond the screens for more blocking of such light. This was said to be especially effective indoors instead of buying the indoor light package. Of course only the smallest attachment to the screens possible should be used to avoid blocking the screens themselves.

17. Just wanted to mention about the Discovery barrels from Crosman. We was talking about them the other day to use on the 2240’s and 1322/77’s.

I ordered one in .177 caliber today. It was \$20+\$4.95 shipping and they say it will come in the mail in 5-7 biusness days. I forgot to ask about the price of the .22 barrel. But here is the part number for the .177 and .22 barrel.

Discovery .117 caliber barrel 1760SE-001
Discovery .22 caliber barrel 2260SE-001

• GF1,

Thank you for the parts numbers. Downloaded the Discovery parts diagram after we discussed this last week. I found a used 1377 that I have on order. I don’t believe that it will be too long before I start adding to it and converting it to a 22 carbine. I can see that my next order will be for a 22 steel breech kit and shoulder stock from PA and a discovery barrel and wide trigger shoe from Crosman. LOL

I like the wide trigger shoes and found that they can be ordered direct from Crosman if you have purchased a CCS gun from them. Here are parts numbers, compliments of a poster on another forum.

Crosman Trigger shoes
Color Part #
Black 2300 012
Silver 2300 013
Blue 2300 015
Red 2300 016

Jim

• I got a brass one with my 2400kt when I ordered it as well as a matching muzzle brake.

• I’n guessing that brass would be the missing one in the parts number string – 2300 014

Jim

• Could be, I don’t remember
I just wanted to let the readers know it was available.

• Jim
Thanks for those trigger part numbers too.

I just ordered me a black 1377 with the 1399 stock for \$79 bucks yesterday as well as the .177 steel breech. It was \$37 if I remember right.

Also ordered 3 new steel spinners too. PA had that 15% off sale and free shipping over a \$149 yesterday and I took advantage of the sale. I’m going to put my Bug Buster scope on it once the Disco barrel gets here. Should be a nice little gun. Yes I miss not having the other one I had a while back. Fun little guns.

18. B.B.,

Thanks again. You get right to the heart of the matter.

If I understand, consistency (as others have already noted) is the most important. Consistency on the part of the chronograph internals, consistency of the setup and consistency of the shooter. If this consistency is there then I expect it will serve well to tune for best performance (not fastest fps) of the air gun in question (particularly PCP’s).

I suppose the first thing is to know why I want this information, knowing it is only one part of tuning particular system or even for better understanding that system (doing some what if adjustments).

When I do use one, I will be very careful to make best use of it because I know where to start.

Thank you, B.B. All I wanted was to find some information on the Titan back in the fall of 2011 and I stumbled into this blog. You are not my only source of air gun info, but you remain my primary source.

~ken

• Ken
But the whole thing that got today’s blog started was results that me and Buldawg got.

He had gotten a few guns from me and his chrony readings are always 75 to a 100 fps slower than my readings when I had the gun and with the same pellets. We both have the Chrony brand chronographs.

So Buldawg asked BB if he would do a report on what could cause different readings. We know how to use them. We wanted to know what the things were that could cause problems getting consistent readings.

So BB has made us all more aware of that today. I believe anyway.

• Gunfun1,

I look forward to hearing from you and Buldawg to know what happens now.

~ken

• Gunfun1,

I don’t doubt for one moment that either you or Buldawg read the instructions and set things up from there. If you guys now diligently set both chronographs up to be as close to the same as can be gotten – then if you guys still get this kind of difference in readings, I will suspect one or both chronographs has a problem.

~ken

19. Probably a flat thin metal ruler could be placed on the side of the eyes pointing straight up. That would tell how their positioned.

And I guess if their point towards each other you could get a faster reading. And if pointed away it could be a slower reading.

20. Wow, this looks to an absolute sinkhole of things that could go wrong. I can just imagine what would happen if I took one out to the range. On the subject of ways of calculating speed for moving cars, I was told that airborne police will time cars moving between measuring points on the road.

Chris, I forgot one other important analogy between slinging and shooting. I just discovered that I have been doing the slinging motion wrong. Well, it took me about 100,000 rounds before I realized that I was jerking the trigger for my handguns, so it’s all consistent.

Matt61

• Matt, you’re correct about airborne speed traps.
On some stretches of road there are big white X’s that they use to time the speed of traffic and relay that information to ground units., if you look for them you’ll start noticing them more and more.
I picked up that tidbit while driving trucks back in the day.

• Matt61 and Reb
They have white lines painted across the highways where I live.

21. Chris USA Chiming back in late! I AGREE with you! I always find room for improvement on anything that I do! Whatever it may be! Never enough for improvements! It never stops! I do tinker myself! I also pay for others to tinker with my own property and improve their own property’s!! Semper fi!

• J.Lee,

🙂 Yup! I pay too, but that is rare. New cars would be an example of that. Roofing would be another. Too old for all that, and in the case of new cars,….too dumb. Can’t shoot my airguns all busted up,…ya know?

22. Hey guys sorry for the late post but have had a busy day.

BB
Thank you for all this very good info and the many different variables that need to be minimized as much as possible to get a consistent and repeatable reading for your particular guns. I learned a good bit and can put it to use now.
I do have one question that I don’t believe you answered or made clear or if so I missed it, but is there a best height to shoot above the eyes as compared to another as the directions with mine stated to use a height of 4 inches above the eyes so I have electrical tape placed on the rods at 4 inches above the top edge of the chrony box ( likely 5 inches above the eyes themselves ) on both the front and rear rods so it gives me a height reference for placing the barrel at as well as a reference as to if the barrel is level to the eyes as well.
So is that a “best height ” or should it be 2 inches or 6 inches. I know it is critical to be as consistent with the setup and gun positioning as possible for consistent and repeatable readings, but just wondered if a certain height is optimal over another random height .

I have a chrony alpha master ( red ) chrony that stays mounted to a tripod that has an adjustable height but no angle adjustment but then I shoot at the same place with the gun on the same porch railing and adjust the chrony height to place the barrel at 4 inches above the upper edge of the box or approximately 5 inches above the eyes since they are about 1 inch below the top edge of the box.

GF1 and me have indeed had issues with the readings we get on our chronys with a gun he has owned or vice versa and have yet with at least 6 or more guns gotten reading of anything closer than 50 fps and as much as 200 fps of each other and it seems the higher the velocity the greater the differences are so this report has given us some more info as to try to remove as many variables as possible between our testing practices to achieve hopefully closer results. I do believe we likely will never truly know the reason until the day comes when we can shoot the same guns side by side on our chronys at the same place at the same time to rule out all variables to do with location and weather.

I know I shoot my chrony with the sunshades always attached and in place outside on my porch in a place where it is never in direct sunlight but in shade and get very consistent readings of as low as 6 fps ES and 2 fps SD with my FWB 300s, my 177 Mrods ( MIne and the one I bought my grandson for X-mas ) both shoot from 900 to 880 fps over a 50 shot spread with a ES of 18 to 20 fps and SDs of 5 to 8 fps so my reading are very consistent and have only had error reading when the battery is getting low in the chrony so I guess I should consider myself lucky in that I have little to no trouble achieving consistent and repeatable results with mine on any given day.

I also agree is not so much the actual number you get but that it is consistent and repeatable that truly matters for the purpose of tuning and testing for a guns improvements after changes have been done or to see if it is degrading from use over time. It is just a tool and nothing more so its up to the user to understand how to best use the tool to gain the most benefit from its use and maintain it to get many years of accurate results from it.

One day GF1 and I will be shooting side by side for just the fun and camaraderie of being able to do it and hopefully that day will finally have an answer to our age long nagging question is it our chronys or our locations that give us inconsistent numbers from the same guns.

Till that day we will just continue to strive for perfection in all our endeavors as best we can.

BD

• BD
How high above the eyes is a good question.

But I have tryed that also. I have shot one shot 10″ above the eyes and the next 6″ then the next 3″. They actually have produced identical readings and have tryed it on another day with the same gun and got 3 or so fps difference than I got before.

I know the photo eyes we use at work have a range of distance they work in. And it’s actually a pretty big distance. Well I call it big. It can see a half inch tall by a 1/8″ diameter part pass by on a conveyor up to 24″ away. But it does take some bracket adjusting to get the eye to see correctly.

Also I have tryed shooting with the he barrel not parallel to the eyes and the readings are always slower. Depending on how much of a angle I have the barrel at to the eyes. I have got up to a 100 fps slower.

I believe that it’s kind of like that tolerance stacking deal we talked about before. I believe the parts and all the other variables combined gives different readings.

And I really think that air density has something to do with our different readings.

But all in all it really don’t matter what reading I get or what readings you get. It does matter though that we did chrony the guns when we got them on our own chronys so we know what results the guns were producing. At that point on that’s what matters. I’m not going to ship a gun back to you or your not going to ship a gun back to me to see what my chrony says or your chrony says. We have our own chronys to get the info needed from those guns.

Kind of just like the Holly carb thing. Just cause we both got the same cars with the same set up. Doesn’t mean that Holly carb will perform the same on both engines. That carb could be ok on one engine and great on the other. Just to many variables for that carb to work its best on both engines.

Probably the only way we will know something. Is if we have both our chronys side by side in the same location and shoot the guns over both chronys.

But at least now we all can try some of the things mentioned today to see how it affects our readings. Write down your readings and note how you had the gun positioned and such. That would be good data to collect too. Then you know what not to do when your chronying. Or at least have some idea’s of what not to do. Just another way to better consistancy with your chrony tool. As they say. There is a right way and a wrong way to use a tool.

• GF1
I did not think the height above the eye is really that critical but was just curious if a given height was better so to speak than another so as to optimize the setup for the best results.

I have not tried shooting at any different height other than say two to four inches over the top edge of the chrony and saw no discernable difference in the reading as well so it likely is not that critical other than just using the same height to be consistent with the setup.

I wonder if the eyes you use at work are of better or lesser quality than what chronys use and I would suspect they are likely close to the same depending on the amount of precision required that they must detect for the operation they are inspecting. I know the photo cells used in cars for year to turn the auto headlights on or off and from low to high beam are quite sensitive to changes in light reception but all have a delay built in to prevent the lights from constantly turning on and off when going thru tunnels or clouds on a partly cloudy day.

I am not ruling out air density either but not sure if it really has as much of an effect as we think it might since we both don’t live anywhere near 3000 plus feet above sea level where the air density really starts to change drastically.

Agreed that the fact that we don’t get the same reading is not as important as the fact we get repeatable reading from the guns and you are correct it would be costly and somewhat pointless to ship guns back and forth solely for the purpose of comparing chrony numbers since there will be one day we can do it side by side.

We at least know that it is likely either a small difference in our setup or test procedures as well as possible location or weather difference on any given day, but can just as easily be that our eyes are 1/8″ or so different in their exact position in the boxes of the chronys or angles since we are well aware of how much tolerance stack ups there are in any mass produced item of the quantities sold by F-1 chrony company.

BD

• BD
Don’t know if price means anything. But one of the eyes at work cost much more than the whole chrony costs. But you know how that goes. They may have the prices marked up.

And when I say density I don’t mean how much oxygen is in the air from being at different sea levels. I mean like if it’s a humid day or not the air heavier or less heavy. In other words thicker. So maybe density isn’t the right word. How about the parametric pressure and air density.

Here is something to look at.
http://www.theguardian.com/notesandqueries/query/0,,-202025,00.html

http://www.mymobilebay.com/stationdata/whatisbarpress.htm

http://www.usairnet.com/weather/maps/current/barometric-pressure/

• GF1
Very good explanation of density and the different effects it has in our environment.

BD

• GF1
I am fairly sure the eyes you use at work are much more precise than what chronys use since they have to be capable of seeing minute differences in distances and shapes whereas the eyes in a chrony only need to see a momentary change in light transmission in their field of view. They may mark the prices up since they are used in manufacturing environments but its likely because they are much higher quality as well.

I fully understand what you mean when you say density as the amount of oxygen has nothing to do with density in the sense of the amount of moisture or thickness of the air and its relation to the basis of measurement being at a standard of sea level.

The first link does not work and the second is a good explanation of what density is but the third link is very informative and interactive and when I just check it the density of where I live and you live at this time are within 1 to 2 points of being exactly the same so right now there is not enough difference in the density of the air to make any real difference in our chronys reading due to the atmosphere at least.

I believe it is a manufacturing tolerance difference between our chronys that give us the inconsistent reading and was wondering if you got the chance to make a rough measurement of the space between the eyes that I did with mine being roughly 12 inches apart.

I have not confirmed that they are in fact pointing up at a perfect vertical direction as of yet but will check that the next time I use it with a square and bubble level.

BD

• BD
Yep that could maybe get it set up better but still they eys might not be the housings right.

But at least you know your setting up more consistent that way.

Let me know what kind of results you get.

And yep I thought the air density links had some interesting info.

• GF1
Just insuring the housing’s are at the correct angle and position is not going to help if the eyes are not aligned in the housings properly that’s for sure.

I am not going to take the housing apart to check for that so will just look into them with a light to make sure they appear secured the same and at the same angles as best as possible.

I at least get consistent reading from the same gun at different times so it is are good to use to compare tuning changes at least and is all that really matters for me.

Yep good info on air density and is updated at least on a regular basis it looks like.

BD

• BD
You know I just thought of something else I do naturally but forgot to mention.

When keeping the barrel level or parallel to the eyes. I also make sure when looking from above the gun I make sure the barrel is pointed straight through the chrony. In other words the pellet passes over the front eye equally side to side as well as the back eye.

I bet if the barrel was to the left of the front eye and pointed to the right of the back eye that would give a slower reading also or vise versa.

That is not something I purposely tryed so I can see the result. But I will the next time I have my chrony out.

• GF1
Same here as I always sight for level as well as inline over the eyes line of sight in the vertical plane.

That’s one reason I prefer to do my tuning before mounting the scopes so I can have a better view of the barrels true position on relation to the chronys eyes since there is no scope to obstruct the view of the barrel and its position.

BD

• BD
The scope don’t bother me at all on the gun when I chrony.

And your not going to believe this but I hold my gun upside down when I shoot over the chrony. I actually rest the scope elevation turret on a folded towel. It kind of gives me a rest with a pivot point to position the barrel as needed. I rest my one hand on the bottom of the stock and pull the trigger by pinching the trigger with my thumb and my pointing finger on the trigger gaurd. It’s just the way I done it forever. And I’m not shooting at a target when I chrony. I’m shooting at a stop about 3′ out past the chrony. So all I’m concentrating on is the gun I’m chronying.

Now you know I’m crazy. 🙂

• GF1
The scopes don’t really bother me but I just find it easier to do the tuning without the scopes since I am not shooting at anything when chronying either just the big tree in my yard as a backstop.

Yea the shooting upside down I will agree is crazy and if it works for you then go for it, but I don’t have the strength in my fingers I used to and would be afraid I would accidently slip and drop the gun. I just use my heart cath bag to rest the gun on and adjust the chrony to the gun so its at the 4 inches below the barrel and keep the gun lined up to the eyes for level and inline with their windows.

BD

• BD
I’m not holding the gun up. The elevation turret is on a towel on the surface that the chrony is on.

So I just use the front hand to steady the gun. And the trigger hand does nothing but pull the trigger.

The scope turret helps me keep my barrel height consistent above the eyes always with that particular gun. It’s a very consistent way to place the gun barrel in the same location with no effort at all.

• GF1
I understand you are not holding the gun up and it is resting on the elevation turret but that is just an 1 inch diameter supporting area which makes the gun very unstable and creates the circumstances for the gun slipping od coming loose form my grip and falling to the ground.

The use of my heart cath bags allows the gun to set in place by itself without any support from me and therefore to me is a much more stabled and takes away any risk of it being dropped or falling unless it is bumped by mistake. It also allows me to adjust my chrony to the gun instead of the gun to the chrony and since my chrony is on a tri pod just works better for me.

You use your chrony with it sitting on a table so I can see how your method is easier for you since it gets the barrel higher than the eyes of the chrony but its just not the easiest way for me to do it and for me resting mine on a bag prevents the possibility of me dropping my guns while testing them .

It works for you but does not for me so I will not change what does work for me, you need to find a 3 dollar tri pod at a garage sale and then you won’t have to stand on your head to chrony your guns . LOL

BD

• BD
Just because I do it that way for doesn’t mean somebody else needs to. It’s just what I tryed and what I’m use to. And I record the gauge readings and watch the gauge so how I can see how much the needle moves per shot. Well on the Benjamin/Crosman guns anyway where the gauge is on the bottom of the gun.

And at least you didn’t suggest that I mount the chrony upside dpwn or from a ceiling so I can stand while I shootside.

But hey I just thought of something. If the chrony is up side down I wouldn’t have to worry about getting the sunshades positioned right. The chrony would be its on sun shade. 😉

• GF1
I know that its just your crazy side showing and meant no offense by me saying I will not do it that way. I generally am not concerned as to how the gauge moves per shot since its not accurate enough to truly tell much from a single shot but just record start and end pressures and divide by the number of shots to get pressure per shot used.

I thought about suggesting you try it upside down but was not sure exactly how to tell you to mount the chrony so it would be stable enough to keep you from shooting it again. You know you are a member of an elite club don’t you its the ” I shot my chrony club “. LOL

You are right the chrony would be it own sunshade and you could even place a mirror under it on the floor to get two readings per shot and save air that way.

BD

• BD
I think we should stop joking around. Somebody’s going to take a seriously.
🙂

But I really do hold my gun upside down on the table with my chrony setting on the table as normal. You know me. Always being different.

Heck look at my bi-pod mounted from the scope idea. And I might add is working out real good on my pcp guns that being the .25 Marauder and the .22 Talon SS. But I should say I tryed it on my Tx and it just don’t work as good for a springers recoil.

Oh and since I’m thinking about it. Did you try the scope on a wrope trick yet?

• BD,

There is no best heighth as far as accuracy of the measurement is concerned. But each chrom=no does have a best height for sensitivity. You just have to work with the machine to discover where they it. If it measures at all, it should always measure the same, regardless of heighth.

B.B.

• BB
Ok cool as that’s what I was wondering and since my chrony gives me good repeatable and consistent readings at the manufacture’s recommended height of 4 inches above the top of the chrony’s enclosure I will continue with that height.

BD

23. Chris USA Yes! “ya know?” When you get too old or beat up to do it yourself for those things plus you listed! I agree also! Plus it really hurts to not be able to do all those things! Eyesight becomes a problem etc! Semper fi!

• J.Lee
No only 60 but the 76 is for my first dog of my own and it being am American Staffordshire Terrier ( AKA Pit bull as the slang for the breed ) born on July 4th 1976 for a bicentennial pup and hence the handle buldawg.

Did almost got in the marines in 74 as I took the ASVAB test and scored a 84 but got a job as a mechanic first and that started my carrier as a turner of wrenches on all thing road worthy.

Due to health reason I can no longer turn wrenches on vehicles so I have found that air guns give me the same satisfaction of working with my hands and creating things that function and perform better than originally intended by the manufacturer. It helps me keep my sanity and enjoy life with limited abilities due to my health limitations.

Semper Fi

BD

25. Buldawg76, Thank you for your reply! I’m late getting back? Like your history with the BD!! I also had a couple BD’s!! My first was almost 70 years ago! Health is very important!! Semper fi!

• J.Lee
Agreed health is no 1 anymore as we aren’t getting any younger. The pit bulls are the most misunderstood breed I think there ever was or still is, they are one of the most loyal and docile breeds around but unfortunately because of there natural instincts of the breed they have been exploited for benefit those who see fit to gain financially from that quality of the breed.

Any dog can be trained to be a killer but very few truly attack the way a pit does with their tenacity and lack of fear. it is the way they attack that has gained then the bad names in the publics eye. It is not the dogs fault any more than its the guns fault it is used in a manner by people that cause the loss of lives as neither one on its own can or will kill people without the training or improper use by people.

BD

26. GF1
Yea someone may get the wrong idea and try what we are kidding about here .

I keep forgetting to try to rope trick when I am shooting and I guess I just need to put the rope I have to use for it on the step out to the porch so I trip over it the next time I go out so I will not forget to try it. You know me I have to strap my mind in it holder to make sure its with me at all times since anymore it comes and goes as it pleases.

I promise one day I will try it and let you know how I like it just cant say exactly when as its raining again today, dog gone it is spring ever going to get here.

BD

• BD
Ok let me know how it goes with the scope on a rope.

And yep we been in the mid 30’s all week again and rain and wind here and there. But lucky timming again. It’s suppose to be in the mid 60’s and sunny this weekend. So I’ll take it. But we’re getting closer to spring. And yep I’m ready for it.

• GF1
Yea the same here with the weather and is going to be a nice weekend as well.

I have a FT match Saturday and think I am going to shoot the 300 junior again this time and see if I can improve my score to over 30/44. if I can beat that then Rob one of our members owes me lunch.

He made a comment at our last match if I could beat my best score with that 300 he would buy me lunch so I intend to eat on him Saturday .

BD

• GF1
That’s the plan is to get a free lunch.

The gun can do it so its all on me.

BD

• BD
Haha,
And you know your right is all I can say.

Good luck. 🙂

27. It seems like I always get to these conversations after everyone else has already left the party.

If the key to quality measurement is consistency, would it be worth building a jig that would minimize the differences in gun relationship to the chronograph and pellet trap. Would also minimize the chances of shooting the chronograph or (?) missing the pellet trap (I’m sure that one’s been done before as well!).

What I have in mind is something like a 2″ X 6″ X 8′ clamped to the top of a sawhorse (parallel to the ground). Fasten the chronograph to the 2″ x 6″ about half way along it’s length. Attach the pellet trap to one end of the 2″ X 6″ with some scrap lumber spacers under it to achieve the right height. Screw a scrap piece of 2″ X 6″ to the other end perpendicular to the main 2″ x 6″ and cut a “U” or “V” shaped notch in it to position the rifle or pistol barrel. The whole thing should keep the barrel of whatever (irrespective of whether it has a scope, open sights or whatever) in the right place to get consistent readings and avoid “ooops’s”. When you’re done, unclamp it from the sawhorse and lean it up against one corner of the garage. Shouldn’t take up much room.