Reading targets – Part 1

by B.B. Pelletier

I’m driving back from the airgun show in Roanoke, Virginia, and am reprinting this article from Airgun Revue #1. It was just a filler when I wrote it for that magazine, but it turned out to be very popular with readers. Apparently, shooters new to airguns and even seasoned shooters don’t always fully understand terms many of us use every day. I hope you find this two-parter helpful.

1: Center-to-center
The most popular way to state group size these days is a measurement of the extreme spread of the group, measured from the centers of the two most distant holes. The measurement is called center-to-center. As with many measurements, this requires some explanation.

Different sized pellets (calibers) will produce different sized groups, all measuring the same extreme distance center-to-center! In other words, a quarter-inch, 5-shot group made by a .25-caliber pellet will be larger than a quarter-inch group made by a .177 pellet.

Using this method, a group size of 0.0″ is theoretically possible.

Although the measuring process requires one additional step (see No. 3), this is the most widely used method because it gives the smallest-sounding group size.

2: Extreme size
Another method for measuring group size is to measure the extreme spread of the group across the widest dimension of the hole. Doing it this way, all groups of a certain size (e.g., 1/2″) will be the same size, regardless of the caliber of the pellets.

It is impossible for group size to be smaller than caliber when this method is used. The method is not as popular as the first method because group sizes will always measure larger.

3: Center-to-center measurement
To measure group size using the center-to-center method, measure the length across the widest group dimension and subtract a pellet diameter. See the above graphic for details.

4: Boxing the target
An archaic measurement method is to give the outside diameter of a rectangle in which the group fits. This was used in the 19th century and the first part of the 20th century, but it has fallen out of favor. It was useful in the regulation of both barrels of a double rifle, but no one uses it for anything today.

5: Cloverleaf
A cloverleaf is a specific type of one-hole shot group in which the shots overlay one another, yet the diameters of each pellet (or most pellets) can still be seen. This is best seen when using wadcutters.

I’ll finish up on Tuesday.

52 Responses to “Reading targets – Part 1”

  • Anonymous Says:

    BB- how was the air gun show? I have a couple questions for you. First of all, have you tried the whisper or super streak in .22? If so how were they? Another question I have for you is how I can get an airgun (Benjamin Discovery). I live in new jersey and have my airgun permit which allows me buy an air rifle at a dealer. However, because so few people have aiggun permits here, I have yet to find one dealer. I was really looking foward to getting this gun but I thing my chances are running low. One more thing is that I have to remind you about the walther falcon review…
    Thanks
    John

  • Vince Says:

    John, there ARE some dealers that will ship to NJ. Unfortunately I can’t name them here for a couple of reasons.

    But I do believe that pyramydair.com WILL ship an airgun to an FFL in NJ, who then will let you have the gun after seeing your permit and recording the transaction. My local FFL in Salem County will do that for $15.

    BTW – never heard of an ‘airgun permit’ in NJ. All I know of is the generic ‘Firearms Purchaser ID Card’. Is that what you’re talking about?

  • FRED Says:

    John,

    there is no problem purchasing airguns in NYS (NYC excluded), CT or PA. I buy most of my air rifles in PA since the ones I want are not carried in any of the stores here in Jersey (from dedicated gun stores like Ray’s on Rt. 22 to Department Sporting Goods stores like Dick’s). It’s in the Gray area of whether it’s legal or not since BATF doesn’t call an airgun a firearm but NJ does.

    BB, great to meet you at the show and thanks for being so generous with your negotiating on the price of your book. It just never occurred to me that I was trying to purchase a “collectible”. I will call one of the dealers there, Ron Saul, who believe he has the handles for my Benjamin Rocket 77. By the way, I reviewed the information in the Bluebook and the operation manual I downloaded from Crosman and my pistol is not modified or “bastardized”. It’s just a later model pistol with the plastic handles.

    One last thing, there is something I’d like to mention to you that I don’t think should be on the blog. What was your e-mail with Pyramid air that we could use to contact you? I forgot it and can’t find it easily on the blog.

  • BG_Farmer Says:

    I use the C-t-C method now, because it is the most common and has the advantage of comparing groups b/t calibers, but it still seems a little indulgent. A 1″ group really ought to fit inside a 1″ circle:).

  • wayne Says:

    B.B.

    Travel safe and enjoy the fall colors on the way home…

    How dumb of me to not know CTC meant center to center… I’ve been measuring outside to outside.. Anyway I agree with bg-farmer that a 1″ group ought to fit inside a 1″ circle.. it just makes sense.. and that is why most people shoot .177 cal in field target.. That steel hole won’t let you subtract the diameter of the pellet…

    Matt61,

    I finally got around to fixing the mag on my Air Arms S410, I don’t know why I waited so long.. it only took 10 min.. It was a little gunky, so I cleaned it up and oiled the parts and she is smooth as silk now. I set up the 25 dot page at the indoor 20 yard range and loaded up 13- 10 shot mags, last night to test it out.. I wanted to see how fast I could work the side lever and stay in decent groups.. Not one miscue on the loading, smooth and quick..

    I got the 130 shots off in just under 13 min.. 10 shots per min…. which includes changing mags.. 7 groups were 3/8″ or less, (extreme size) 10 groups were 3/4″, including the last one that was a 10 shot group… and the rest in between..

    So, Matt, don’t let the magazine issue stop you from getting the AAs410 .177.. you won’t be sorry..

    Wayne,
    Ashland Air Rifle Range

  • Anonymous Says:

    BB is there a “Standard” among airgunners as to the number of shots, or the distance to the target? From SavageSam

  • wayne Says:

    SavageSam,

    I think the standard is 5 shot groups, and people just state what distance they shot them at.. But I don't know, that is just what I've heard.

    B.B. can tell us tomorrow, when he gets home..

    Wayne,
    AARR&R

  • Anonymous Says:

    RE: 1″ group into 1″ circle

    A 1″ group into 1″ circle does fit with ctc, but using the centers as the reference point, not the outside edge of the pellet. The whole point is that precision shooters are so good that it really makes a difference. In others words, the ctc method removes the “penalty” of the pellet size.

    When I spray pellets with my Crosman G1 subtracting the diameter of a pellet is insignificant. However with my Daisy 22SG the pellet diameter is significant to the group size.

    Herb

    PS – BB, reading your articles is like eating potato chips. Can’t wait for the next one!

  • B.B. Pelletier Says:

    Fred,

    I am so glad you found out about your .177 Rocket gun. Now you will believe me when I tell you that I don’t know everything about airguns. Having a Blue Book handy is a powerful aide.

    You can write me care of blogger@pyramydair.com. I normally don’t answer those, but I;ll see the message and be able to respond.

    B.B.

  • B.B. Pelletier Says:

    John,

    I haven’t tried the Whisper in .22 but those who have say it really doesn’t do justice to the caliber. The Super Streaks are having such quality issues that I really cannot recommend them. I expect the .22 to be very powerful in that rifle.

    Others have answered the New Jersey question.

    B.B.

  • B.B. Pelletier Says:

    SavageSam,

    Your number of shots question deserves a whole blog of its own. Five is the most common number. Ten is used by professionals for reasons I will explain in the blog. Three is used by beginners who are not aware of statistics, and by makers who are trying to represent their guns in the best light.

    B.B.

  • Anonymous Says:

    bb,
    Type in Berkut 2002 in google, search images (its all in russian). IT EVEN HAS A REAL BARREL bushing,double action/ single action, decocker, steel slide, 22rnd mag in .177 cal and about 420fps with its five inch barrel. The gun is only 7.5 inches long. I looks real comfortable.
    Shadow express dude

  • BG_Farmer Says:

    BB,
    I’d be interested in the 5 vs. 10 or more rnd groups blog as well…I learned long ago that 3 shots can really lead you astray, but never had a good idea of where to stop. One of the first things I do when I get a new rifle or ammo is shoot a “box” of whatever it takes to get an idea of the “circle of confusion” (term I borrowed from optics). Sounds pointless, but it seems to be a pretty good rough indicator of how the rifle will perform long term.

    On the other hand, I guess it really doesn’t matter for me, because I have a bad habit of screwing up the next to last shot, no matter how many I intend to use in the group…This is so consistent for air rifles and firearms for me that I am thinking about self-hypnosis:). I would be interested to know whether there is a magic number that encapsulates all the possibities for a rifle or if the group size expands indeterminately forever.

  • Mr B. Says:

    Afternoon B.B. My brain is saying that any way of measuring a group’s size that gives an answer that is smaller than the diameter of the projectile just doesn’t make sense to me or a 1/4″ group with a .177 pellet is smaller than a 1/4″ group with a .25 one. Sounds like the old which is heavier the lb of feathers or iron. Mr B.

  • Lloyd Says:

    B.B.,
    I like to use a pair of inexpensive digital calipers to measure groups. First I open the calipers up to the pellet diameter I’m shooting and push the button to reset the zero on the calipers. Then I can measure outside to outside and it displays the C to C dimension. No math needed!

    BTW, it was a pleasure meeting you and the other bloggers and folks in Roanoke, including your photography and field target buddy, Mac. Great fun!

    Lloyd

  • Kevin Says:

    BB:
    Will it wreck my HW50S if I shoot the Eun Jin .22 Cal, 32 Grain pellets from time to time, just for fun? I just bought a tin of 100 and thought I should ask first.

    I really enjoy everything you write, and buy supplies exclusively from Pyramyd in support of your efforts here.

  • wayne Says:

    bg-farmer,

    Try what I did last night and practice firing quicker, the first time the cross hairs cross the center, or better still on the way up, just below, at the last split second..Tell yourself your just practicing, and testing the gun or pellets, not your skill level…Bottom line, just relax, let go of muscle to control any part of the process.. Try to let it become automatic.. Then when you take a little more time to slowly approach the center, the flyers lessen..
    Anyway, that has helped this novice improve groups a lot…I learned that by testing guns, and breaking them in, not expecting good groups for the first 500 or 1,000 shots…

    Wayne,
    Ashland Air Rifle Range

  • Anonymous Says:

    B.B.

    Yes, tell us about the show.

    N.J., I feel for you. The laws are even more restrictive than California.

    Wayne, if you’ve been reporting actual group sizes then you’ve been selling yourself short, and your groups have been that much better than you’ve been reporting. Thanks for reporting about the mag fix for the S410. My faith is restored.

    Matt61

  • B.B. Pelletier Says:

    Shadowe Express Dude,

    That pistol is the A-3000 Skif under a new name. The Skif has such a bad rep. they cannot sell it by that name any more.

    I wondered if that were the case, since this is Anics.

    Thanks for the warning. I did the Skif A-300 here:

    http://www.pyramydair.com/blog/2006/09/anics-skif-a3000-co2-pistol.html

    Read the report, re-read the ad copy and you’ll see what I mean. I will not review this pistol. I don’t advise getting it.

    B.B.

  • B.B. Pelletier Says:

    BG_Farmer,

    There is a magic number indeed. It comes to us from the world of statistics. I will explain what I have observed about group shot sizes over the past 40 years.

    Don’t want to say more now or I will start the report!

    B.B.

  • B.B. Pelletier Says:

    Mr. B.,

    You are correct – a 1/4″ group of .177s is actually smaller than a 1/4″ group of .25s, when using the center-to-center measurement. That’s why some shooters like the outside diameter instead of ctc. But customs are hard to kill and ctc has the advantage of making caliber immaterial.

    B.B.

  • B.B. Pelletier Says:

    Lloyd,

    Your measurement system is great! I may try it if my el-cheapo caliper will allow it.

    I enjoyed our discussion at Roanoke and know we will be talking again!

    B.B.

  • B.B. Pelletier Says:

    Eun Jin,

    That’s a real stretch – putting those heavy pellets in such a light powerplant. I don’t think it will hurt, but those who say heavy pellets are bad for springers probably would. Since I don’t know everything, I’d advise caution in this case.

    B.B.

  • B.B. Pelletier Says:

    Matt,

    As all of you have guessed, I’m back home a day early. I drove straight through – 1130 miles in 20 hours. Ouch!

    I will start the show report on Wednesday. Not trying to stall, I just need some time to work with the pics.

    Remember, there will also be a video, later.

    B.B.

  • Anonymous Says:

    Kevin,

    Couple tuners say that too heavy a pellet can damage a Springer. B.B. does not follow that same school of thought. I would guess that bad boy at about 415 fps?

    Anyone,

    My two cents, if you don’t take the diameter of the projectile into consideration, you could have five cannon balls in the same hole but still call it a 9” group.

    Volvo

  • wayne Says:

    B.B.

    Glad your home safe..what did you get me daddy?…..

    The video will be a treasure for those of us who have never seen such a thing..
    Ouch is right, that’s a long time in the saddle partner… and nice mph if you stopped at all to pee..

    Wayne,
    Ashland Air Rifle Range

  • wayne Says:

    Volvo,

    Amazing, how we often comment at the same time..one min apart..

    That is a great counter to my idea that the size of the field target hole won’t allow center to center measuring.. the outside edge of the pellet has to fit inside the steel hole…. or no score, unless you get very lucky, with a bounce off..

    But really when shooting a cannon ball, the rules are for cannon ball shooting and when shooting Field Target the rule is to knock down the target, (with a certain tool) not make a 4′ hole in the ground…

    So maybe we can have different measuring devices for different situations…

    Wayne,
    Ashland Air Rifle Range

  • B.B. Pelletier Says:

    Wayne,

    I’m an old man. I didn’t stop to pee. I just drove fast between the bathrooms!

    B.B.

  • wayne Says:

    B.B.

    That's what I thought, but we better not tell anyone…

    When I delivered my pagoda bird feeders to stores like "Wild Birds Unlimited" & "Wild Bird Centers", I would fill up the Volvo wagon and trailer, and drive 1,200 to 1,400 miles in 30 hrs stopping to make a few deliveries.. once a week, hurrying back to make more for the next week..

    that's when I was a work-a-holic instead of a shoot-a-holic…

    Wayne

  • twotalon Says:

    Wayne….
    Have you ever seen or made bullet proof or shatter resistant bird feeders?
    I can’t find a plastic one that don’t crack and fall apart when accidently hit. Harder plastics are just too brittle.
    I have a wooden one with a steel plate in the end, just in case.
    Even then, I shot it off the hanger while trying to kill a starling. I hit the suspending cable squarely and ripped it right out of the feeder. The frags got the bugger, so it wasn’t a total loss.

    twotalon

  • Mr B. Says:

    twotalon:What a great idea–pellet proof bird feeder. How about the cylindrical style made out of either metal pipe or possibly industrial heavy PVC depending on what gun you’re shooting. I’ll check my pile of “junk” and see what I can come up with. B.B. I haven’t forgot the report I owe you on the Talon SS with the 24″ barrel and bloop tube. I am still waitng for the barrel. Mr B. PS Looking fwd to the report on the show.

  • Anonymous Says:

    OK, Airsoft shooters…here’s one for the books:

    I put a Crosman P50 airsoft pistol in my pocket. It fell out and hit the concrete floor. It didn’t work after that. I tried everything I knew to get it to shoot. Then I had a bright idea. I dropped it on the concrete again, from about two feet. Now it works!

  • wayne Says:

    TwoTalon,

    You know the biggest problem people had with bird feeders was squirrels eating the tray sides to get a larger opening for their mouths.. So we offered a copper faced tray side on a custom basis.. I would think a 600fps .22 cal would dent it, but not hurt it.. We had removable glass panels, so if you hit one, you could have replaced it.

    We had a lot of people tell us they shot squirrels off their feeders, it's a very big problem..

    They make steel tube feeders, just like the plastic ones.. they would probably work, for keeping them from eating them and pellet proof as well…

    Wayne,
    AARR&R

  • .22 multi-shot Says:

    Aren’t groups meant to tells us how accurately a shooter and gun performed? If this is true, then center to center is the best method of measuring.

    If you draw a line for a pellet’s path of travel, that line would probably indicate the path of the center of the pellet (more generally, center of mass since the pellet may tumble, etc.), not the edge of the pellet. When you use edge to edge, not only are you using the edge of the pellet as your reference, but you are switching edges depending on where the pellet hit!

    With ctc, group size indicates deviation of the strike points. A group size of 0″ clearly indicates that you are shooting the exact same place over and over. If you don’t use ctc, what does a group size of 1/2″ mean? You don’t know unless you know the caliber.

    Ctc just make more sense to me. Just my 2 cents. :)

    .22 multi-shot

  • Anonymous Says:

    Wayne,

    Copy and paste the link above. Few action shots of Tom.

    Volvo

  • twotalon Says:

    mr b.
    Thin metal would be OK. at least it won’t shatter. Rubber would be good. Both would take a beating without falling apart. Don’t want anything too heavy.
    Maybe some aluminum flashing put together with pop rivets. So it gets ventilated…at least won’t shatter.
    Talons and plastic bird feeders do not go well together.
    Open to suggestions.

    twotalon

  • twotalon Says:

    Interesting ideas Wayne.
    It will have to stand repeated strikes and /or passthroughs from a TSS without falling apart too fast. A little duct tape to cover the holes so the food don’t run out should handle it.
    May take some beer, but can probably come up with something .

    twotalon

  • agathokles Says:

    Hi, B.B.

    I’m trying to understand how, in essence, the gas-spring powerplant differs from the single-pump pneumatic.

    As I understand it, the gas-spring system, when cocked, pressurizes gas within it. When the trigger is pulled, the gas is allowed to expand, pushing a piston (which would otherwise have been pushed by a mechanical spring), and this piston, in turn, pressurizes the air that drives the pellet down the barrel.

    With a single-pump pneumatic gun, cocking it pressurizes air; when the trigger is pulled, the pressurized air is allowed to expand against the pellet, driving it down the barrel.

    So, the only difference I see between the gas-spring and single-pump pneumatic is the intervening piston in the former, which seems an unnecessary complication — i.e., you have compressed gas pushing a piston to compress air to drive the projectile. What am I missing, here? Thanks.

    == agathokles

  • wayne Says:

    Volvo,

    Thanks,
    Those are great pics. I would sure like names to the faces.. Maybe Tom will give us some reference..

    Guess what, I traded the Evanix AR6 for a FX Timberwolf 22 cal. two shot version.. I'm thinking it will be more collectible and accurate, even though it's not a six shot like the AR6…

    I was told it's your Webley Raiders twin sister… I found I can get a moderator for it, and it will screw onto the BSA Lonestar as well.. At least that is what I was told.. I'll keep you posted.. I know you would like your Raider to be less noisy…….

    Tell your wife what a great deal you got compared to me… Already you could double your money…

    Wayne,
    AARR&R

  • wayne Says:

    .22 multishot

    You and Volvo are absolutely right, except in Field Target. I have to measure my groups outside to outside when practicing …. because the pellet can't touch the edge of the steel hole and still be sure to knock down the target. That is why most everyone uses .177 cal for FT.

    That steel hole is not the same as paper punching.. where center to center is for sure the way to go.. Then you can shoot cannon balls and .177 pellets in the same contest… just use different air guns…I would think..

    Wayne,
    AARR&R

  • Anonymous Says:

    Wayne,

    You’ve got me beat again. The Timberwolf has a Lothar-Walther Barrel is Power Adjustable.

    I think they are a similar style and size, plus both are two shot models.

    Hope you enjoy it.

    Volvo

  • wayne Says:

    Volvo,

    Someone told me they were both made by FX.. I thought they were the same.. Well I didn’t beat you anyway, you paid about $200 less than my straight across trade for the AR6… but thanks for making me feel better about it.. I think the Timberwolf has a gauge too… There are some neat videos on Utube of the Timberwolf in action, that is what got me to do the trade..

    Wayne,

  • Anonymous Says:

    Bg-farmer,

    I’ve found I do better when I aim at the numerals on the Gamo targets, for example I’ll shoot groups at the number 4’s. I started this to get more use out of a target, but noticed a trend after awhile. I think aiming at a bulleye is more pressure than an arbitrary spot.

    Let me know if the hypnosis works, and I’ll give it a try also.

    Volvo

  • Anonymous Says:

    RE: Squirrels & Bird Feeder

    Made myself an industrial strength feeder out of 3/4 inch pine to bait squirrels so that I could get them in a good position to shoot. The front (On side which I shoot) is overlapped 3/4 pine, glued together, with grain running in opposite directions. I put clear plastic underneath so I could see if feeder was empty, but not hit it with a pellet.

    Herb

  • Anonymous Says:

    agathokles -

    I’ll jump in and try to give you an answer. With a pneumatic gun (PCP or pump) a chamber is pressurized, then when the trigger is pulled a valve opens to release the air down the bore. So the tiny valve is the only part of the gun moving (besides the air.)

    With a regular springer, the spring and the piston are moving when you shoot which is a lot of mass. So there is more recoil which is problematic because the pellet is traveling so slowly that it isn’t out of the barrel when the recoil starts to move the gun. The springer also had a nasty backwards recoil when the piston reaches the end of its travel, which destroys scopes that are not specifically designed for a springer air rifle (thus you could mess up a great firearm scope by putting it on a springer).

    With the gas-springer the spring is replaced with a gas piston. When you cock the gun you are compressing gas inside the sealed gas spring. Thus the mass of the spring and piston is replaced by the piston rod of the gas spring and the piston. Still get a lot of recoil since a lot of mass in gun is moving.

    Herb

  • Vince Says:

    agathokles – I think you were asking ‘Why bother with the piston at all in a gas ram? Why not just go with a pneumatic action?”

    I think the answer can be illustrated if you ever tried driving a nail. Fairly easy to do with a hammer, but isn’t the hammer just an unnecessary complication? Since your hand pushes the hammer and the hammer pushes the nail, can’t you just get rid of the hammer and push the nail in?

    We can usually accelerate something more quickly if we wack it rather than push it.

    The springer and gas ram gun turn stored energy into momentum – like a hammer. The fairly heavy piston rushes forward building up a lot of velocity, and near the end of its stroke the pressure of the air pocket ahead of it spikes very high very briefly. Ideally, that’s when the pellet will start moving (and not before).

  • B.B. Pelletier Says:

    Mr. B.,

    No rush on the guest blog. Just whenever it’s convenient.

    B.B.

  • B.B. Pelletier Says:

    agathokles,

    You have misinterpreted the gas spring mechanism. It’s purpose is not to compress uncompressed gas when the gun is cocked. It compresses gas that is already under some compression, and raises it to a higher state of compressions.

    It is nothing like a single-stroke. It is identical to a coiled steel spring-piston gun, except that compressed gas drives the piston instead of a coiled steel spring. Read this report:

    http://www.pyramydair.com/blog/2006/04/gas-springs-of-theoben-airguns.html

    B.B.

  • agathokles Says:

    BB (and others):

    Thanks! I’ll study up on gas springs, and perhaps I’ll have additional questions; but for now, I appreciate all of your responses.

    == agathokles

  • ajvenom Says:

    Most of the time I use 5 shot c-t-c. I like using c-t-c because it’s easier to compare your shooting from one cal to the next. If I have a consitant set up I will move to 3 rounds sometimes.

  • Lloyd Says:

    Backstop and bird feeder materials-

    My experiences don’t have to do with feeders, but with the safety of some of the materials mentioned today.
    When I was a kid I shot a tractor tire and the BB bounced back and hit me a half inch below my eye, just like Ralphie in Christmas Story. So be careful with hard rubber.

    Then recently I was unwisely backing up a target with a piece of Trex deck material. My .177 Gamo 1000 imbeded the CPs nice and cleanly in the Trex, but when I tried my .22 B40, the pellet bounced right back at me. Another idea for the bad list.

    Just my 2 cents.
    Lloyd

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