## Friday, October 19, 2007

### Why are there TWO zero points when sighting in a scope?

by B.B. Pelletier

First, let me say how nice it was that so many of you who have never commented with your names did so yesterday. It's nice to know you are out there. I was really surprised that so many of you responded. Thanks!

Today's post was suggested by Lego-man, who didn't understand where the two zero points for an airgun scope came from. I would normally have directed him to the post on determining the range at which to zero your scope, but that was where he asked the question. So, the words weren't getting the idea across. And, if one person asks, there are 10 more who don't bother to. Today, I'll draw some diagrams.

Here is the question: Ok..Im new to this air rifle thing, How do you get 2 distances from one scope? Also what is the best kind of range to zero in at?

The answer to this question, or I should say the science behind the answer, is obvious once you understand it. But until that time, you might wonder why I keep talking about two sight-in ranges.

Once a bullet leaves the muzzle of the gun, it starts falling to earth. How the barrel is oriented to the ground (i.e., is it pointed up so the bullet first rises, or is it parallel so the bullet drops right away) plays a large part in determining how long it takes the bullet to hit the ground. But gravity always wins. Even when the bullet appears to be rising away from the earth, gravity is still acting on it to pull it down. And, I expect everyone knows all that.

You probably also know that bullets, typewriters and Jell-O molds all fall at the same rate. If our gun barrel were exactly parallel to the earth and if a bullet were dropped beside the gun at the moment it fired, both bullets (the dropped one and the fired one) would hit the ground at the same time. The fired bullet would be some distance from the muzzle of the gun when it hit, but it would fall at the same rate as the bullet that was dropped.

For this discussion, I'm omitting subtle aerodynamic forces, such as the Magnus Effect, that could actually change the time of the fired bullet's impact by a miniscule amount. Certainly these forces do exist and do affect the flight of a bullet; but for the purpose of this discussion, I'm overlooking them. I don't believe their contribution amounts to enough to consider.

One more thing you all know is that bullets, and especially diabolo pellets, slow down the farther they travel from the muzzle. The farther they go, they more they slow down. That makes the pellet's path curved toward the ground; and the farther out you go, the more curved it is.

Now I'll show the first graphic.

All I'm showing here is a visual of the pellet's trajectory described above. The scale on these graphics is way off, because 5" wide is all Blogger allows as an image size. Look at them for the relationship, not as an exact representation.

If you understand the first graphic, let's see what the scope and open sights are doing while the gun is firing.

The scope is mounted above the rifle, and looks straight out to infinity. What we have to do is realign the scope so it coincides with the trajectory of the pellet.

Graphic No. 2 is also easy to comprehend. The scope looks straight while the bullet is always dropping. What we need to do is adjust the scope so the two can work together. Once again, it's important to understand that this compressed drawing is really played out over many tens of yards of distance. Here's the final graphic.

The scope has been adjusted to look downward through the trajectory of the pellet. This is done when the rifle is zeroed. The range at which the rifle is zeroed is that first point where the straight line of sight and the curved trajectory coincide. At that spot, the pellet will be striking the target at the same place the crosshairs are resting.

Obviously, the graphic is way out of scale. In real life, the amount of downward slant is very minimal on most airguns. In fact, if you don't use adjustable rings, the scope itself isn't slanted, but the erector tube inside is. On some of the Dianas that use an adjustable scope mount, you can actually see the scope pointing down. But it does point down on all airguns, because if it didn't, you could never hit the point of aim.

Do you see that the pellet now appears to rise above the line of sight? Of course it doesn't, but that's what it seems to do. And then farther out it seems to drop back to the line of sight once again. Now you understand what is actually happening is that the pellet is always dropping. By aligning the scope as we did, it only appears to rise and then fall.

If you go back to that old post of mine, you'll see that I give the advice to make the first intersecting point 20 yards from the firing point. Then velocity will determine where the second point falls. With a rifle that has 900 f.p.s. velocity at the muzzle and is sighted-in at 20 yards for the first intersection, it will intersect again at around 33-35 yards from the muzzle. You have to test on a range to discover where it will actually strike - and that's true no matter what your velocity.

The amount the pellet "rises" above the line of sight with this method is about one pellet's diameter or less. That gives you a zone of 20-30 yards at which your rifle is zeroed without any scope adjustment.

This type of zero works for airguns at close distances and is due to the separation between the scope and the barrel. If you zero an airgun at 50 yards and farther, you can kiss off this technique. Field target competitors stumbled on it because 20-30 yards is where many of their targets are located, so they learned to sight-in this way.

I hope that's now clear to everybody.

At October 19, 2007 7:52 AM,  Anonymous said...

one of your examples mentions sighting in at 20yrds for a 900fps rifle. what if you have a rifle that shoots around 550 fps, should you still sight in at 20yrds? i realize the second intersection point would be less than 33-35yrds. what would be the optimum "zone...at which your rifle is zeroed without any scope adjustment for the 550 fps rifle?
thanks

At October 19, 2007 8:18 AM,  Anonymous said...

B.B.
Have you already done the review of the 460 Diana in 22. cal.? If so where is the link.

At October 19, 2007 8:25 AM,  matt said...

Hey BB,

I've listed the following link before, but it has fantastic demonstrations of zero points:

http://www.arld1.com/trajectory.html

I hope readers take a look if they need further explanation. The site has been very useful for my own understanding.

And thanks to you for your dedication!

Matt

At October 19, 2007 8:54 AM,  Anonymous said...

BB -

Long time reader first time poster. Of course my first post would be off-topic!

Here recently I have been rabidly shooting 10M in my basement, pistol and rifle. My TAU 200 absolutely loves Schak 4.48 pellets. Rested on a rail-mounted wire bipod and using the TAU peep, it will put 5 Schaks inside the 9 ring. I am astounded by the performance of this rifle/pellet combination.

I was under the impression that the Schak was simply a practice pellet. Do you have any idea what the "match" version of this pellet is? Not that I need it, just curious. I am still struggling to keep it in the black off-hand, so its not the pellet!

Thanks for the time and effort you put into this blog. Every morning I get my coffee, log in and hit your blog to learn something new. Great way to start the day.

Will

At October 19, 2007 8:59 AM,  Anonymous said...

i think i might have answered my own question. at 550fps, 20yrd sighting is probably still optimal. i probably have a zero zone out to 25-27yrds.

550fps

At October 19, 2007 9:11 AM,  B.B. Pelletier said...

550 f.p.s.,

I'm glad you answered this question because I can't. I haven't done any testing on velocities this low, with regards to scope zero points.

I do think so empirical testing is needed before we agree that 20 yards is optimum. If you are in a position to do it, why don't you become our leader?

B.B.

At October 19, 2007 9:13 AM,  B.B. Pelletier said...

460 Diana,

No, I haven't tested the .22 caqliber 460 yet. It's on my short-term to-do list.

B.B.

At October 19, 2007 9:18 AM,  B.B. Pelletier said...

Matt,

That's a good site - thanks for the link.

His graphic is better and larger than mine, but he has the rifle elevated and the scope looking straight. I show the same thing, only I didn't elevate the barrel.

I think an animation would be the best way to show this.

Who out there can help me with video animations?

B.B.

At October 19, 2007 9:25 AM,  B.B. Pelletier said...

Will,

The SCHaK is made by JSB. They tend to produce the most uniform pellets of any maker, so it's no surprize those pellets are good.

Try the Match Diabolo by JSB and also the H&N Match (or the Beeman H&N Match, whichever it cheaper).

I'm glad to hear that your TAU 200 is performing so well.

B.B.

At October 19, 2007 9:44 AM,  Anonymous said...

B.B.

I have a somewhat related question about sighting in. I've read your method about three distances for sighting in a rifle at 20 yards--10 feet, 10 yards, and 20 yards. My question is if you want to sight the rifle in at 20 yards why not stay put there? I can see that the other method will work by adjusting the point of aim, but it seems like a hassle to keep changing distances and I don't see the benefit. Thanks.

Matt

At October 19, 2007 11:10 AM,  Vince said...

Matt, I think BB suggests starting out at 10 feet just so that you are on the paper immediately... saves a lot of time trying to figure out where a pellet is going if you're completely missing the target (which sometimes happens to me at 10 yards with a newly mounted scope).

Of course, BB will correct me if I'm wrong...

At October 19, 2007 11:40 AM,  Anonymous said...

Thank you, Vince, that makes sense to me. I have never sighted in at that distance and hadn't thought of that.

Yet, another related question for B.B. and anyone else who has information. I don't have access to a reliably measured range of 10 meters, so I'm trying to relate the group sizes I do get to that distance. Is there a rough generalization of how group size changes with shooting distance? (I know there are many factors involved. Say for 600 fps if that's helpful.) I recall a post by B.B. somewhere saying that this relationship is non-linear. In other words, you cannot assume a gun that will shoot a half-inch at 25 yards will group in one inch at 50 yards. The B.B. post said that pellets spread out more at around 35 yards. Could I assume roughly linear until that point? Are there other critical points where things change? The curved trajectory diagrammed in today's posting is suggestive but since that depicts the change in aim point, I don't see that I can really deduce the change in accuracy from it.

Matt

At October 19, 2007 12:57 PM,  B.B. Pelletier said...

Vince and Matt,

Yes, 10 FEET is a great starting point. When I worked at AirForce and had to sight-in a customer's rifle after service, I could do it this way in under 10 minutes after the scope was mounted.

Ten feet, then 10 yards, then 25 yards (which I see as the center distance of a 20-30-yards sight-in. All I had at the old AirForce factory was 23 yards, but that was close enougth.

Matt, as to your other question, I really haven't done enough testing to say for sure what size groups to expect at what distances, but here is a general observation.

A good rifle will group under 0.10" at 10 yards/meters; under 0.25" at 25 yards and at or under 0.50 at 50 yards.

HOWEVER, having said that, I have just tested a prototype PCP that groups identically at 25 and 50 yards on a calm day. I cannot tell you what was happening, but it did so in both .177 and .22 and it did so for many groups. So sometimes stuff happens that defies explanation.

B.B.

At October 19, 2007 1:13 PM,  Vince said...

Matt, again BB will probably be able to add more useful information - but one thing that becomes more of an issue at longer ranges is variance in velocity.

Remember that (vertically) the pellet is basically in freefall, which is very closely approximated by the equation D=16*T*T, where "T" is flight time to target, and "D" is the distance that the pellet drops.

Obviously, flight time varies with velocity... but the amount that the pellet drops is that variation squared. If (for example) average velocity to target varies between 900fps and 950fps, at 10 yards the 950fps pellet will drop about .19", while the 900fps shot will drop about .21". The vertical spread due to velocity change will only be about .02".

Move the target out to 20 yards, using the same average flight times, the drop now becomes .77" vs. .85"... and the spread is now .08" (4x as much). At 30 yards, it grows to about .2". At 50, we're over 1/2". I'm oversimplifying the math, as I'm not taking into account the deceleration of the pellet due to air resistance. Regardless, this effect is obviously very non-linear.

This is one of the simpler reasons why accuracy is non-linear over large changes in distance... I'm sure that BB can add others.

At October 19, 2007 2:16 PM,  Anonymous said...

Finally a topic I might have a bit of input, instead of always questions.

I believe it would be good to remind that the height of the scope from the barrel will have an effect on the zone.

At October 19, 2007 2:17 PM,  SquirrelKiller said...

Hello B.B./Tom,

Just an off topic observation as usual:

Just got my BAM B30-1 in .22cal today. Is this Chinese rifle a sleeper or what at \$169? Only shot about 50 rounds through it to gauge speed before I decided which scope to mount, and getting 750fps with 14.6gr H&N's, and appears very accurate so far with open sights out of the box. It doesn't appear to be hold sensitive either, maybe due to its weight and girth. At 18.24ft/lbs, its my most powerful "springer", and modestly priced. My .22cal CFX only shoots 650-675fps at best with same pellet, and accurate as well.

Unless I got lucky and got a good one, the BAM has a nice finish to the wood and metal. Only problem I had out of the box was a loose/short rear trigger guard screw which I had to replace with a longer identical one from my tool box, and tightened all the other receiver-to-stock mating screws. One thing I will need to watch is the rubber/plastic (?) from the cocking-lever pivot appears to be flaking from rubbing on the automatic safety switch. Sice-cockers aren't as graceful looking as their underlever counterparts on the cocking side of the gun, but the price helps me see past that.

So far I can't believe I only spent \$169 for this rifle. Now I understand your statements about the B40. My eyes are open to these Chinese rifles, but time will be the telling factor, or maybe I got lucky. Maybe I will get a B40 in the future...

Take it easy, and take care, and as always thanks for your efforts.

At October 19, 2007 2:19 PM,  Frogman said...

B.B.

How can you tell whether you are hitting the target with the first intersection of the sight line and pellet trajectory or the second? Is there a way to tell other than trying it at another further range without adjusting the scope?

thanks

At October 19, 2007 2:32 PM,  Anonymous said...

Thanks, B.B., for the response. So, the old MOA criteria still holds good. Vince, thanks for your observations about how gravity relates velocity spread to group size. I had heard that velocity spread was a crucial determinant of accuracy and now I know why.

Matt

At October 19, 2007 3:42 PM,  Kevin said...

BB,
Just when I found a writer even better than TG..... :)

Question:
What pellet or bb gun do you recommend to train an 8 year old girl?

Starting with her 4th birthday, she has shot from time to time (with me supporting the weight). Now she asks all the time, so I guess she is ready. My 46m and P1 are both still too heavy for her.

I see on Pyramid that the that the NRA has named the Walther PPK/S as their youth training recomendation.
If that is also your recommendation, can I use lead perfect rounds for safety in that gun?

kap

At October 19, 2007 3:42 PM,  B.B. Pelletier said...

Scope height,

Yes, but with most scoped rifles, that height falls within a narrow range.

B.B.

At October 19, 2007 3:47 PM,  B.B. Pelletier said...

SquirelKiller,

I haven't tried the B30 yet, but yes,the Chinese, and especially BAM, are right there when it comes to value. You just have to pick the model carefully.

B.B.

At October 19, 2007 3:50 PM,  B.B. Pelletier said...

Frogman,

In my opinion, there is no way around actually shooting at the distance at you wish to sight in. I have seen computer programs that were supposed to interpolate for you, but I've never seen one that came out right on target, except possibly by accident.

B.B.

At October 19, 2007 3:53 PM,  B.B. Pelletier said...

Kevin,

There is only ONE gun on the planet for you - the Daisy Avanti 499. Buy the special ground shot with it, and targets and a Crosman 850 BB trap. Don't forget safety glasses for everyone. And get the optional diopter rear sight if you can.

She will love it and so will you.

B.B.

At October 19, 2007 3:54 PM,  Anonymous said...

The Tech Force 89 Contender, what are the odds you would get a good one?

At October 19, 2007 4:12 PM,  B.B. Pelletier said...

TF89,

I can't say. I only tested one, but I've heard lots of good things about the AR 1000 which is the same rifle. And I have heard nothing bad yet.

Do a search on that model name and see what turns up.

B.B.

At October 19, 2007 4:18 PM,  Anonymous said...

Hey B.B.

I was reading about a sniper rifle in Popular mechanics magazine today and it said that the rifle only had a 10 power leupold scope (leupold m3a to be exact). Now it said that the .308 caliber rifle was accurate to about a mile. While on the topic of scopes I wanted to ask why don't snipers use higher power scopes? I seem to remember you saying snipers usually stay around 10x but can't remember why. One would think that they would use a higher power scope (say 20X and up) for shots at such distances. I figured you're the best person to ask considering you were in the army and an overall gun genius.

Thanks, Kyle

At October 19, 2007 4:24 PM,  B.B. Pelletier said...

Kyle,

Military snipers usually don't care where they hit their target, so a smaller more rugged scope will win over a larger more fragile one. They used 20X scopes in the Civil War, but they were really fragile!

There is a lot of fiction about taking a target out with a head shot at incredible distances, and don't think it can't be done, perhaps at 300 yards. But no military sniper is going to worry about such precision in 99 percent of their jobs.

HRTs might be more reliant on that kind of precision, but they don't shoot a mile.

However, field target shooters HAVE to hit in the right place or it doesn't count, so they are the big users of powerful riflescopes today.

B.B.

At October 19, 2007 4:29 PM,  Anonymous said...

B.B.

Good point. Remember reading about snipers and how they care more for just a hit rather than a more risky head shot from a few Tom Clancy books. Thanks.

Kyle.

At October 19, 2007 5:10 PM,  Anonymous said...

10x - mil dot system comes into play as well. Also easy to do the math.

At October 19, 2007 5:25 PM,  B.B. Pelletier said...

10X,

Thank you. I never thought of that.

B.B.

At October 19, 2007 5:50 PM,  Anonymous said...

One opinion of my own... The closer the center of your scope is to the center of your barrel.The less of a lift you will have between the front on target and the back on target points and the less it will move off target as the shot becomes closer to you from the front on target point. In other words, high rise mounts cause larger impact movements as the target range changes. This of course is more obvious in high powered rifle shooting than air riles. But it is still there.I hope that made sense.

Doug

At October 19, 2007 7:10 PM,  Vince said...

BB, I did have trouble with my AR1000... accuracy would not settle down, other than that it was a pretty nice rifle. When I pushed a pellet through the barrel I could feel some bad rough spots. Long story short - I ended up adapting a Gamo Shadow .177 barrel to the breach block, and now it shoots pretty well.

Unfortunately, I now suspect that a good cleaning with JB paste might have been all it needed! In any event, it was an interesting excersize trying to get a replacement barrel for it... I called the factory in China, who told me to call Air Gun Inc in TX, who told me to call Compasseco, who told me to contact the factory in China. So parts support isn't what it could be.

I did try swapping the barrels from my Hammerli Storm and my Beeman S1 into the AR1000 - they were both a perfect fit. Uhnfortunately, a replacement barrel from RWS or Beeman would have cost far more than what I paid for the gun!

I am thinking about trying another example (in .22)... but I'd give it a good cleaning first!

At October 20, 2007 2:13 AM,  Anonymous said...

bb,

just out of curiosity, since we all know who you are, does this mean you will stop posting gun reviews on the tips and tricks section pyramydair? i always enjoy reading em. one more question for you...who are those reviews so spaced out? those only happen once every few months. i really like the videos at the end of some of the articles...i personally think you should keep doing both...and also, is there any chance we'll see any full video gun reviews in the future? after all, actions speak much louder then words, lol.

DED

At October 20, 2007 2:35 AM,  Anonymous said...

bb,

im looking into getting a mountainair modded qb78 .25 with full barrel shroud, but its bulk fill only, and im not very knowledgeable with co2...what would i need to fill the gun from 20 oz co2 tank?

DED

At October 20, 2007 5:18 AM,  B.B. Pelletier said...

Doug,

Yes, the closer the center of the scope to the bore, the less angle there is to overcome. What that does is help make the spot over which the pellet shoots more or less flat, longer.

Unfortunately, with an airgun-type scope that has a large objective lens, you must mount it high enough to clear the gun, which is why I said they all fall into the same catregory.

With a firearm and a smaller scope you get a large flat spot, but with an airgun that shoots so close and a much higher scope (for clearance) the flat spot is reduced.

B.B.

At October 20, 2007 5:19 AM,  B.B. Pelletier said...

Vince,

That sounds like an awful lot of trouble and expence to fix the rifle.

Did you ever try cleaning the original barrel?

B.B.

At October 20, 2007 5:45 AM,  B.B. Pelletier said...

DED,

Everything will continue as before. The articles and the blogs will not change.

And, yes, there will be longer video reviews of some guns in the future.

B.B.

At October 20, 2007 5:46 AM,  B.B. Pelletier said...

DED,

B.B.

At October 20, 2007 10:27 AM,  Anonymous said...

I was just considering a gun with a large objective with a low mount with a lower comb would make a difference compared to a gun with the same scope mounted with a high mount on a high comb.

Would be interesting to see a blog on that.

What is the difference in velocity or number of shots using Co2 or air? A modded Crosman 2260 looks interesting, anybody have any experience with that?

At October 20, 2007 11:21 AM,  Anonymous said...

Congrats on the new freedom of not trying to maintain your "cover"...
must have been a realy power drain.

Anyone who's watched you answer almost identical questions repeatedly any patiently can tell you have the spirit of a teacher

BTW is there any way to get my login info sent to my email...hate being anonymous and have forgotten it since I had login problems a long while back.

Here from the begining, here to the end,
Turtle

At October 20, 2007 1:06 PM,  B.B. Pelletier said...

Turtle,

I don't know how to get that information, I'll see if our IT people can help.

B.B.

At October 20, 2007 1:39 PM,  Anonymous said...

bb,

do you know if if pyramyd will sell the superstreak in .22? i want to reserve one, but they only have the .177 right now.

DED

At October 20, 2007 1:58 PM,  B.B. Pelletier said...

DED,

I'me sure they will when Crosman starts making them.

B.B.

At October 20, 2007 3:03 PM,  Anonymous said...

bb,

I posted this in the RWS forum but I'm sure you can answer this.

"Does anybody notice after or possibly during firing a shot from a break barrel
that the barrel droops down? Not a lot just enough to see that it isn't straight.
In my case its a 350. It seems that the ball detent mechanism that locks the
barrel is not holding the barrel straight after the shot. I can see how the
hard kick of a magnum springer would loosen the lock but is this loosening after
the pellet has left the barrel? I was thinking my O-ring for the barrel was
shimmed too much and the ball detent wasn't latching properly but the shots are
all hitting where I want them to. Although if the scope is centered to take this
drop of the barrel into consideration then I guess it isn't a problem.
Exactly how tight should that lock be?"

At October 20, 2007 5:21 PM,  Anonymous said...

hi bb
would this hold true for open sights as well? im guessing it would. also is there any harm i can do my barrel be shooting a pellet backwards? im thinking giant hollowpoints.

Nate in Mass

At October 20, 2007 5:26 PM,  B.B. Pelletier said...

The lock should be tight enough to do exactly what it's doing.

If the ball bearing lock makes the barrel hard to open for cocking, it is correct. As I recall, that kind of lock doesn't have or need an adjustment. The secret is in the spring tension and in the ball itself.

You can do a test. Put some baby powder, talcum powder or flour on the joint of the rifle after it's cocked and fire the gun (with a pellet loaded, of course). There should be a small puff of air made visible by the powder. All the powder should not be blown off the top of the gun.

B.B.

At October 20, 2007 5:29 PM,  B.B. Pelletier said...

Nate,

The principle holds for open sights, but since they are mounted so much closer to the axis of the bore, the number change a lot. The flat spot is much longer with them.

You can shoot pellets backwards, In fact, there used to be pellets that were MADE backwards just for that purpose.

I'll blog them next week.

B.B.

At October 20, 2007 5:53 PM,  Anonymous said...

If you shoot your pellet backwards you will commit suicide.

At October 20, 2007 6:18 PM,  Anonymous said...

thanks bb
im interested to see what you mean.

to the guy above me, i shot them at a very low velocity for a test. i made sure to roll over the skirt slightly so they would feed eisier. i retrieved one from a bottle and the skirt had folded perfectly back onto the head. obvioisly they are not very accurate but i was thinking it might work good at closer range, or if you didnt have hollowpoints and needed some. they didnt penatrate too well though. im afraid to bump the velocity up though because it might vause too much wind resistance or problems in the barrel.

Nate in Mass

At October 20, 2007 6:24 PM,  B.B. Pelletier said...

Nate,

I think he was trying to make a joke.

B.B,

At October 20, 2007 6:45 PM,  Anonymous said...

oooooooo

hahaha

i get it

thats funny

Nate in Mass

At October 20, 2007 7:17 PM,  Anonymous said...

BB,

Thanks for all the great hours of learning.

I have one variation I'd like to understand. So now I have my rifle zeroed in at 20 yards, which was sighted with a parallel target. Now I'm going to shoot a squirrel which is 20 yards away, but 10 yards up a tree. How should I compensate for the fact that the target is elevated? How about if I'm shooting down hill?

I can't seem to visualize the difference elevation makes on the targeting.

Seems like I'm a pretty good shot at a parallel piece of paper, but struggle to hit a target up a tree or down a hill.

Thanks
LaughingSquirrels in St. Louis

At October 20, 2007 7:33 PM,  Vince said...

BB, with regards to my AR1000 - Yes, I DID try cleaning it. With valve grinding paste. 'Nuff said.

Didn't go through a lot of expense fixing that barrel (the one I eventually used was a takeoff from a Shadow I converted to .22), but trouble? You have no idea! I wanted to bore the barrel and fit a liner, eventually I found that a 1077 barrel would make a perfect liner. Then came the "boring" part - and several hours later, it didn't come out straight. I got the liner in, but you could tell that it "snaked" as it went down the barrel!

Several times I was sorely tempted to throw in the towel... but the gun was fairly new, and I couldn't bear to do that. Besides, other than the accuracy it was a nice rifle - smooth, powerful, delightful trigger.

Yes, in retrospect, a good cleaning with JB and a bronze brush might have taken care of it. Live and learn, I guess....

At October 20, 2007 11:39 PM,  Anonymous said...

LaughingSquirrel, you could try an electronic rangefinder for the range. As to up a tree or down a hill, imagine a squirrel was straight up or down from you, and do the diagram above and see what you decide keeping in mind gravity.

Or there are rangefinders now that will figure it all out for you, range taking into account angle.

At October 21, 2007 4:29 AM,  Anonymous said...

Hi B.B. I recently got into springer airguns after 30 odd years of using CO2 and then multipumps.

My springer is a few months old. I've fired about 2000 pellets so far.

I noticed my power dropping off (no chrony) so I disassembled the gun. What I found (as I suspected) was a worn synthetic seal. I compared it to a new one and there was a noticeable difference in the diameter of the seals.

The gun was copiously lubed from the factory.

I polished the internal parts, installed the new seal, lubed, and re-assembled. The gun now fires better than it was new.

Question is, is there a guideline regarding how often we might expect to change the synthetic seals on springers.

If you need to know, the gun is a Crosman Phantom.

By the way, I had a sneaking suspicion it was you all along.

Thanks.
Phantom Shooter

At October 21, 2007 9:00 AM,  Anonymous said...

This is LaughingSquirrel.

I don't think my question is about range finding. But rather the effects of changing the elevation of the gun on my sight picture.

Anonomous said imaging shooting straight up. Good example. The pictures BB provided in this blog should change as the pitch of the gun is changed (or do they?). I'm trying to understand what that change is. The impact of that change.

As I pitch up do the sight intersections move foward/backward.

At October 21, 2007 9:05 AM,  Anonymous said...

Hint: If you shoot straight up or straight down there is no "drop" as there is horizontally.

At October 21, 2007 9:15 AM,  Anonymous said...

BB,

How many consistent shots do you get with 1 powerlet on Crosman 2250? Thanks.

At October 21, 2007 9:37 AM,  B.B. Pelletier said...

Laughing Squirrels,

If he's 20 yards away but 10 yards up a tree, shoot as if he were only 18 yards away. Aim high, because the slant range places him closer.

Your pellet drops less going up or down than it does going straight.

B.B.

At October 21, 2007 9:39 AM,  B.B. Pelletier said...

Vince,

There's not much harder than boring a deep hole straight.

B.B.

At October 21, 2007 9:43 AM,  B.B. Pelletier said...

Phantom Shooter,

2000 rounds is awfully short for a piston seal. They should go at least 10K rounds anf I've heard of some going 50K rounds.

It depends on the material the seal is made from and the condition of the compression chanber.

With what you have done, you should last another 10K rounds.

B.B.

At October 21, 2007 9:44 AM,  B.B. Pelletier said...

2250,

I would be guessing 40-50.

B.B.

At October 21, 2007 1:15 PM,  Anonymous said...

hey bb,

i have a daisy 880s and it does not have any lock a 50 pumps! No air was in for a second shot It shoots 7.9 CPs at 830 like w/ 50 pumps! 100 fps faster than 10 pumps.

Any thoughts?

-sumo

At October 21, 2007 1:22 PM,  B.B. Pelletier said...

sumo,

That is one remarkable 880.

B.B.

At October 21, 2007 1:26 PM,  Anonymous said...

Hi bb,
I have a Theoben Eliminator. Which do you thing is the best distance to zero my gun? I like to use it for long range hunting.

At October 21, 2007 1:38 PM,  B.B. Pelletier said...

Theoben,

That's a question only you can answer. I zero all my smallbores at 20 yards,

B.B.

At October 21, 2007 2:34 PM,  Anonymous said...

sumo,
at some point i dont think you can get the air at a high enough pressure to even go into the valve. like the pressure in the valve and outside(of the pump) become equal. youll probly start wearing doen the mechanism pretty fast if you keep doing it. just a thought.

Nate in Mass

At October 21, 2007 6:52 PM,  Vince said...

Yes, BB - boring a long, straight hole. But the operative word is "straight", and doing by hand without the correct bit really didn't work out.

In retrospect, if I had spent \$30 on an 18" long 5/16" bit, it probably would have worked out. But I can get stupidly cheap sometimes.... and this definitely was one of those times.

BTW - did you ever get the B50 to shoot? As I remember, you were gonna let it sit for a while and try again.

At October 21, 2007 10:20 PM,  Anonymous said...

Nate,

i hope you dont think i would make a hobby out of pumping a gun 50 times to take one shot. Out of that gun the one shot is still only going into a 1 inch group at about 5 yards(not exact). A 392 is far more accurate and more powerful with only 8 pumps.

I cant understand how this \$35 junker can push 12fp.

-sumo

At October 21, 2007 11:11 PM,  Anonymous said...

phantom shooter,

i have a g-1 extreme, and after about 1750 shots, the velocity almost halved, so i got it tuned from cdt, and he said it was because of extreme detonation...there were many things wrong with the spring area, because of this...crosman tends to overlube their guns, so that is why your seal probably didnt work very well any more(btw, since it was turbotuned, it shoots like a dream...and its not at all hold sensitive...ive tried a veriety of holds, and at 30 yrds, it shoots exactly where i point it, everytime). bb, what could i do for this if i had a new gun(thinking about the tac-1), without spending \$180 tuning it?

oh, also, the grt-III trigger installed on the g-1 makes shooting it a dream, lol

DED

At October 21, 2007 11:16 PM,  Anonymous said...

That was very interesting. And now I understand why it appears to move up but does not really.I want a chrono graph and I came across one that uses your computer and a mic. Have you tried this one? It look interesting and the guy sound really helpful.
http://talonairgun.com/forum/viewtopic.php?t=436

Sheldon

At October 22, 2007 1:25 AM,  Scott said...

DED,

I'm with you about the GRT-III trigger.
I believe that Gamo should put Bob, aka CharlieDaTuna, on their payroll.
;-)

At October 22, 2007 5:55 AM,  B.B. Pelletier said...

Vince,

No, I never got the B51 to shoot. It seems not to accept a charge.

B.B.

At October 22, 2007 5:57 AM,  B.B. Pelletier said...

DED,

How about buy a gun that doesn't have these problems? Like an RWS Diana 34 Phantom?

B.B.

At October 22, 2007 6:04 AM,  B.B. Pelletier said...

Sheldon,

It's an interesting use of a laptop computer, but beyond that, it's sort of useless. Kind of like using the fan from a V8 engine to cool a room. Instead of a thousand-dollar laptop, why not just use a hundred-dollar chrono that's dedicated to the job?

B.B.

At October 22, 2007 11:43 AM,  Anonymous said...

B.B.

I guess because we all have a computer already? and would no cost anymore \$\$\$. I down loaded it and it seems good and easy to use. Not bad for free since I already have a computer. Shoot I even use the calculator on my PC and calculators only cost \$8 but I am using a Dell instead. I think I will save my money and use the free software for now. Free is good.
Thanks for answering my question. Did you like the way it gave you a graph? I thought that was cool.
Sheldon

At October 22, 2007 11:48 AM,  B.B. Pelletier said...

Sheldon,

I guess you're right. Everyone who owns a laptop can use this. No problem there.

The graph is interesting but may be too much information for me. I just want velocity and simple statistics.

B.B.

At October 23, 2007 1:04 AM,  Anonymous said...

bb,

are you going to take it apart to see if you can fix it, or get a new one, since you may have gotten a defective gun, or is that the end of the b-50 review?

DED

At October 23, 2007 6:25 AM,  B.B. Pelletier said...

DED,

I have decided to return the B51 to Pyramyd and let them fix it. I really don't have the time for that.

I hope to get another one to test in the future.

B.B.

At October 23, 2007 11:31 AM,  scott298 said...

From Scott298--when sitting in there are two items I always count on. The 1st is a portable bench rest(which has been discussed in previous blogs) and the 2nd is a surveyors tape which plays out to 100 yards. With the 1st I can set up a shooting area where ever there is enough land and with the 2nd I know exactly at which range I am zeroing in at and it gives me the ability to play around with diferent yardages so I know what my gun is doing and what the hold over of the shot should be at greate distances other than 20 yrds. Picked up the tape at the home depot for under 15 bucks and it is always in my shooting box when I leave the house

At November 14, 2007 8:45 AM,  Zevtov said...

BB.
O.k., I think I am going to have to move to an airrifle. I have been hoping that a more powerful (and not so expensive) airpistol would come out, but the chipmonks, crows, and squirrels are taking over the yard. I might even consider taking some rabbits if I can find the right gun. I (as you have mentioned) have limited funds and have been watching your recommendations. I have around \$200 to spend (I know not much!). I like the looks and what I've heard about the BAM B40 in .22 (I'd like .22), but I couldn't find where you have reviewed the Beeman SS1000T. How would that compare to the BAM B30. As a sidelever, it would seem the BAM would be a bit more accurate than the Beeman which comes with a scope, and can be gotten in a dual caliber, .177 and .22! The Beeman is also break-barrel. Or is there a third alternative?
Michael in Georgia

At November 14, 2007 11:15 AM,  B.B. Pelletier said...

Michael,

BAM B40 is first. The B30 is potentially second, though I have yet to test one. And the 2-barrel Beeman is probably fifth, though I haven't reviewed it, either.

If you want a third alternatoive, think about the Diana RWS 34 Panther.

B.B.

At December 18, 2007 2:27 AM,  Jon said...

gday, i must say I LOVE THIS SITE
Anyway, i dont want to waste anybodys time but ive recently got my first air gun its a CFX mounted with a 4x scope
im just trying to figure out all the trajectory stuff and am just wondering, if i sight her in for 20metres so im right for up to bout 30metres, then how much drop will i need to compensate for at 40m? metres?
cheers

At December 18, 2007 9:35 AM,  B.B. Pelletier said...

Jon,

Expect about a 1.5-2 inch drop at 40 yards. But always test it with measured targets. No tables or computer programs are accurate enough to get the drop precisely.

B.B.

At January 27, 2008 2:14 PM,  mike said...

i am having troubles sighting in.. i get 5 to 10 shots to shoot tight and then they start to scatter everywhere... and then when i click the adjustments up one ot twp i get good groups again and then then scatter

At January 27, 2008 7:18 PM,  B.B. Pelletier said...

Mike,

This sounds like a holding problem. Are you shooting a spring gun? Are you using the artillery hold?

Also, if you have the elevation dialed up high, the erector tube could be floating.

I need to know more about the gun you shoot.

B.B.

At January 28, 2008 3:47 PM,  Anonymous said...

my gun is a crosman quest 1000.. my elevation adjustments are not high to the top. i am using a bsa 4x32 rifle scope.... one question on artillery hold when you establish this hold are you supposed to be seated or standing...

ps: sorry for posting my past comment twice, i am just really frustated..

At January 29, 2008 6:08 AM,  B.B. Pelletier said...

Quest,

The artillery hold is used in a rested (seated) position, only. I think you need to study that technique, because if you don't know it you are loosing all the accuracy your rifle has.