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Air rifle accuracy testing
Posted: Fri Jan 26, 2007 12:33 pm
by Paul
Let's say that I have 3 brands of pellets that group the same from a match air rifle at 10 meters. In order to know exactly for sure which brand is better, would it make sense to test the accuracy of the pellets at a longer range (say 15 meters or 50 ft) ?
Posted: Fri Jan 26, 2007 1:47 pm
by jrmcdaniel
No. What works best at 10M is what works best. I can guarantee you that accuracy does not improve with longer distances when using wad cutters. In fact, I get better accuracy using 10.2grain domed pellets in my 10M pistol at 10M but cannot use them in competition.
Best,
Joe
Air rifle accuracy
Posted: Fri Jan 26, 2007 1:58 pm
by peepsight
Hi Paul
The simple answer is 'NO'
You need to know what the grouping is at 10 metres not 15m. I suspect that a tight grouping pellet at 10 m may well show some enlargement of the group at 15m. So this will not be a good way of selecting a pellet for 10m!!
Peepsight
Posted: Fri Jan 26, 2007 5:43 pm
by Lee Sellers
I think what Paul is asking is whether it would be easier to see a difference in group size by shooting a longer distance. Longer distance equates to more linear dispersion hence an easier time discerning a difference in performance between very similar pellets. In other words, the spread in group size would be easier to see.
This would hold true until the pellet begins to destabilize due to air resistance slowing the projectile. Match rifles, even the slow ones, generate enough velocity for the pellets to be stable at 15meters so the exercise may be telling but for the following:
If performance at 10meters is so close that you can not discern a difference, there is a myriad of issues that will increase your score/performance that are more important to focus on than pellet selection. Even if you were to note an infinitesimal difference in one pellet over the other by shooting groups at the longer distance, will this make a difference on the regulation target? I sincerely doubt it. Once you find a pellet that will solidly hold a 10 quit fussing around and work on the areas that really cause dispersion in your group, like hold, sight alignment, trigger manipulation ...........................etc...................etc........................etc..............
Hope this helps!
Posted: Fri Jan 26, 2007 11:41 pm
by WaltherWill
Once you find a pellet that will solidly hold a 10 quit fussing around and work on the areas that really cause dispersion in your group, like hold, sight alignment, trigger manipulation ...........................etc...................etc........................etc..............
Can't say it much better than that!
Posted: Sun Jan 28, 2007 8:42 pm
by TWP
I've tested quite a few air rifles for kids in our club. We have a nice assortment of pellets, test them through the guns using an Angie Rest. After we test from our batch we order some new pellets of the same size/brand and re-test the rifles. If they still shoot well they order several sleeves of the same lot number to use in their rifle.
So far I have found a brand/size of pellet for every rifle I've tested that would shoot 10 shot groups no larger than a single pellet hole.
The whole process takes a couple of hours. After that the shooter has a couple year supply of pellets.
I think the ability of the shooter is more important, but when you reach the upper levels of shooting the type and size of pellet can make a difference of a few points in a match. Why not use every advantage you can?
If you have 3 brands that shoot equally well at 10 meters then pick the one that is cheapest.
Posted: Tue Jan 30, 2007 9:22 pm
by Florida
Just remember this: An object in motion stays in motion until acted on by some other force... meaning that there is no way in personally known physics that a pellet that does better at 20m than another pellet will do WORSE at 10.
Same with big rifles... There are 'accepted facts' of old surplus military rifles shooting 3MOA at 100 yards and 1.5MOA and 600, which can't physically happen.
So yeah, if you really wanna be able to measure accuracy, don't be afraid to stretch it out. If you can't measure your accuracy dif at 10m, let's say your hole is .178-.180" for a 3-5 shot group or whatever with ALL the pellets you test... you don't really need to stretch out but if you want to find out what is technically more accurate (irrelavent info but fun to take another few steps backwards) then yeah, that's what I'd do.
Of course in order to really do this correctly you have to make sure your fundamentals are down... basically holding still. Breathing, heart beat shaking the gun, etc. But whatever you do DO NOT test off of anything but a decent rest... that can be anything from a rucksack stuffed with dirty clothes in the prone position to a high-dollar rest, but whatever it is make SURE that you are doing this perfectly and that your shooting is not the problem with the gun's accuracy.
Respectfully.
Posted: Tue Jan 30, 2007 11:48 pm
by Lee Sellers
Florida wrote:... There are 'accepted facts' of old surplus military rifles shooting 3MOA at 100 yards and 1.5MOA and 600, which can't physically happen.
Really now? What about precession? Ever hear of the principal of a projectile "going to sleep" What about the fact that gyroscopic stability peaks downrange and not near the muzzle? How about the effects of gas ejecta and base stability? Of course a pellet does not suffer this but what about the trans-sonic effect?
Your known physics differs greatly from mine. I'm glad my Palma rifle doesn't know what you know! <grin>
Compensation
Posted: Wed Jan 31, 2007 10:19 am
by Rutty
Same with big rifles... There are 'accepted facts' of old surplus military rifles shooting 3MOA at 100 yards and 1.5MOA and 600, which can't physically happen.
Well this is a bit off-topic as the original question was about air rifle accuracy and I'm a smallbore shooter. Anyway something stirred in my memory and on the bookshelf I found the following:
Target Rifle Shooting, Reynolds & Fulton, Pub. Barrie& Jenkins 1972
ISBN 0-214-20172-4
Chapter 2, pp27-28
Compensation. Compensation is the term used to descibe the effect of barrel movement in the vertical plane.
The vertical position of the vibrating muzzle when the bullet makes its exit depends on the bullet's travel time in the barrel; and this depends on the bullet's initial velocity and the amount of friction it has to overcome. Variations in these two factors will cause bullets to emerge from the barrel at slightly differing angles of elevation.
A fast bullet leaving the barrel during an upward vibratory movement quits the bore earlier and therefore at a lower point in the barrel's movement than a slower bullet. It also has a flatter trajectory. The point at which the trajectory curves fot the fast, slow and medium paced bullets intersect is called the "compensating range" of the rifle. The grouping capacity of the weapon will be better at this distance than at any other as the effect of velocity variation is eliminated.
By contrast, the rifle which discharges its bullets during a downward movement will not compensate. The faster bullets will leave the barrel at a higher point than the slower, with the result that the two trajectories will move progressively further apart as the range increases. This is known as "negative compensation".
A rifle that compensates can only do so at one particular distance, and for this reason some rifles give consistently closer grouping at long ranges, than at short, and vice versa.
[The paragraph then goes on to describe the method of establishing the "compensation" of a particular rifle]
So maybe Lee's Palma rifle knows something after all!
Rutty