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Thread: Pellet weight revisited part 3

  1. #1
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    Default Pellet weight revisited part 3

    So I have done some more testing on Pellet wt and this time on a "proper" pellets like you guys suggested on the pellet wt post last month. The pellets tested are Air Arms Field. The average wt is 5.546 g as compared to 5.547g as on the pack, at last someone got the weight right. The ES of pellet wt, however, still leave a bit to be desired (but better than CZ/Kovohute lux,DN/RWS geco and way better than Gamo). The lightest pellets can have 3.3% less wt than the heaviest one in the tin. In theory, this translates to about 26ft/s difference in velocity between the extremes (I am so not going to put 100 pellets through a Chronography, mine hasn't got a printout thing). Attached see the distribution. So much for people claiming an ES of 10ft/s (some chronography round up the velocity to the nearest 5ft/s anyway). Most of us do a 5 shot group and this isn't a good indicator for either velocity nor accuracy, if you randomly pick 5 only there is a good chance you will find 5 pellets with very similar weight and then once in a while you get a flyer due to more extreme wt differences and have no idea where it came from.........I am going to some ultratech or maybe JSB next.


    ave 0.546g 8.426gr
    min 0.537g 8.289gr
    max 0.555g 8.566gr
    ES 0.018g 0.278gr
    SD 0.005g 0.076gr


    g gr
    0.554 8.551
    0.555 8.566
    0.555 8.566
    0.552 8.520
    0.541 8.350
    0.538 8.304
    0.547 8.443
    0.553 8.536
    0.545 8.412
    0.544 8.397
    0.543 8.381
    0.545 8.412
    0.552 8.520
    0.544 8.397
    0.551 8.505
    0.543 8.381
    0.541 8.350
    0.541 8.350
    0.548 8.458
    0.541 8.350
    0.539 8.319
    0.538 8.304
    0.543 8.381
    0.555 8.566
    0.548 8.458
    0.542 8.366
    0.537 8.289
    0.554 8.551
    0.543 8.381
    0.543 8.381
    0.550 8.489
    0.547 8.443
    0.541 8.350
    0.540 8.335
    0.542 8.366
    0.546 8.428
    0.546 8.428
    0.547 8.443
    0.542 8.366
    0.555 8.566
    0.548 8.458
    0.550 8.489
    0.542 8.366
    0.553 8.536
    0.553 8.536
    0.550 8.489
    0.548 8.458
    0.547 8.443
    0.540 8.335
    0.540 8.335
    0.541 8.350
    0.553 8.536
    0.543 8.381
    0.552 8.520
    0.547 8.443
    0.542 8.366
    0.541 8.350
    0.539 8.319
    0.542 8.366
    0.542 8.366
    0.545 8.412
    0.551 8.505
    0.550 8.489
    0.547 8.443
    0.554 8.551
    0.540 8.335
    0.546 8.428
    0.544 8.397
    0.547 8.443
    0.543 8.381
    0.542 8.366
    0.548 8.458
    0.538 8.304
    0.553 8.536
    0.548 8.458
    0.544 8.397
    0.549 8.474
    0.548 8.458
    0.541 8.350
    0.550 8.489
    0.540 8.335
    0.548 8.458
    0.549 8.474
    0.548 8.458
    0.549 8.474
    0.548 8.458
    0.540 8.335
    0.539 8.319
    0.549 8.474
    0.547 8.443
    0.550 8.489
    0.555 8.566
    0.551 8.505
    0.540 8.335
    0.548 8.458
    0.549 8.474
    0.540 8.335
    0.539 8.319
    0.540 8.335
    0.546 8.428[br][img:width=200&height=123]../../Deadlinks/public/1152524233_357_FT0_aa_.jpg[/img][br]
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  2. #2
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    Your graph looks like my targets used to on my Hatsan before I cleaned out the barrel...

    Thank you for the very useful information, I'm sure this only reinforces why most serious shooters only use the Air Arms pellets.
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  3. #3
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    BTW while having fun with my PC, the 26ft/s makes a big difference,

    Say we take a rifle tuned for 800ft/s with AA field for 11.97ft/lbs and try to hit the target at 40m.


    At 787ft/s, it takes 0.16675s to travel 40m while at 813ft/s, 0.1614205s. With the equation.

    D = 1/2 X G X "time squared"
    G = 9.8m/s

    With the slower pellet, it would have dropped 0.136246m and the faster one at 0.1276768m, A whole 8mm difference!! Please note that air resistance, earth centrifugal force (good thing don't get that much down south) and the spinning action of the pellet are neglected (don't know how to). But even if the difference is halfed, it could mean the difference between a miss and a hit.........

    I am going to shoot FT for the 1st time in 2 weeks time, if (when) I get my butt kicked, I will just blame my pellets instead of admiting the lack of skill.......
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  4. #4
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    Stopper,
    Come shoot with me. You will have a good chance to win., and do the kicking
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  5. #5
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    Good work Stopper. I just want to point out one more thing that will influence POI wrt to weight differences and that is barrel movement or barrel vibration. The sweet spot of your rifle is very critical and the slightest of variances can have a severe change in your rifle's perfomance. Maybe not that much with pellet guns as with large bore rifles but you will have an effect.

    You might just find that with a lighter (faster) pellet your POI can be lower and vice versa. The other day I shot a couple of shots with my chrony attached to the barrel and my rifle shot like a shotgun and about 30mm high at 25m. I will agree that you will eliminate flyers if your spread of pellet weights are very small.
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  6. #6
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    Francois, you are spot on about the vibration. That's probably why some guns are less sensitive to wt difference, even same model from the same production line. If pelletgun are like firearms, the barrel will move in a figure of 8 motion and if the slower bullets happen to exit the barrel when it is pointing upwards, this maybe just compensate for it. That's why they say we must test all kinda projectiles until we find the best one.

    And then when it comes to barrel movement, Centerfire handguns and rifles with slowish and bigish bullets, say, 444 Marlin 45-70, it is well known that the faster bullets usually shot lower (in short ranges anyway) because the gun starts to recoil and point upwards before the bullet exits. due to recoil. But like you say, small guns probably do not suffer the same effect.

    All in all, small ES = less painful. I wonder if the top world class guys wt their pellets with a 4 digit scale and sort them out accordingly, after all, it onlt takes 15min/tin. I know the center fire brenchrest guys do that, so do some people who cast their own handgun bullets (at least they don't need a 4difit scale to pick up a 0.5% difference in 158gr bullet).
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  7. #7
    Protea FT Team '08

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    [quote1152604047=Francois]
    The other day I shot a couple of shots with my chrony attached to the barrel and my rifle shot like a shotgun and about 30mm high at 25m.
    [/quote1152604047]

    I have had the same thing with my chrono.I however miss low by 50+mm at 27m.I think it has something to do with the way the chrono disturbs the air as it comes out the barrel.

    Do you think with the speeds and weight of pellets we shoot you get vibrational problems.I think my vibrational aim has more to do with missing
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  8. #8
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    I know I know, Marksmanship is the #1 thing, but like they say, we are suppose to test the limit of the shooter, not the rifle. If you can shoot a gourp as big as the FT target round hole and find range right, you will get 100% but add another 4mm varation, you may just miss half of them. Also, it has to do with knowing the gun and ammo you use. All I am doing is to try to get to know my pellets and guns, have a better understanding, practice still makes perfect.

    Besides you gotta give us something to blame on, when the buck is missed, the most popular reasons are (in this order):

    1) bloody scope/sight
    2) bloody ammo
    3) bloody stock not fit
    4) bloody wind
    5) bloody trigger
    6) bloody rifling twist
    7) bloody barrel length
    8) bloody cheap guns
    9) Bloody glare
    10) bloody bipod
    11) Bloody no time to practice

    It is strange that all this problems are gone when they are not shooting, the rifles are now state of the art with the best scope and ammo for the purpose......

    Very few people I know will admit that they need to practice more. Most hunting rilfes in the country are shot less than 50shots/year. Even pellet guns are seldom shot more than 2000 round/year.

    It is very sad but true, it is not those shooters with the best guns that kick my butt at practical shooting, it is those who shoot a lot (meaning most of them at the club) who do.
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  9. #9
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    Allan:-

    Although barrel vibration might be less with airguns as with large bore rifles I believe that it will still have an impact to some degree.

    In rifle you have a number of factors causing barrel vibration and there will be a few correlations between the big guns and airguns.

    The sound waves caused by the release of the trigger mechanism causes small amplitude waves running up and down the barrel. You must remember your airgun shoots aproximately 800ft/s = 244 m/s. Sound waves in steel travels at a speed of about 15000ft/s. Depending on the length of your barrel this sound wave will travel 12 - 15 times up and down the barrel before the pellet exits. This sound wave may not have the biggest influence but it is there.

    There are a lot of other sound generating mechanisms in rifles and if you start adding the harmonics together you get some very interesting waveforms running up and down your barrel.

    The bigger influence is cause by the pressure wave generated by the ignited powder and in airguns by the release of the compressed air into the barrel behind the pellet. This compressed air causes longitudinal pressure as well as transversal pressure waves and the effect this has is a donut like ring running up and down your barrel as well. If you shoot at different velocities the pellet may exit the barrel simultaneously with one of these rings and will cause a flier. As soon as you attach something to the barrel the dynamics of the barrel changes causing different POI.

    This is just a quick one I am throwing into the pot here. There are a lot of things to take into consideration for accuracy but the bottom line still remains. It all depends on the finger. The changes are you will "bewe" more than the effect of the above but it can cause a miss in a marginal shot.
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  10. #10
    Sharp Shooter
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    Some interesting ideas.

    To be honest the effect of the release of compressed air into the bore is unlikely to cause a measurable influence on the barrel, unlike firearms the pressures are negligible.

    There will be vibration along the barrel length, allowing the barrel to behave unimpeded seems to give best results, hence why many pcp barrels ride on an o-ring within the barrel collars. This allows the natural vibration of the barrel while protecting it from undue knocks.

    In terms of the pellet weight effect, the next phase will be to record the velocities returned from known pellet weights and also how the difference in pellet weight affects point of impact.

    Dale
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  11. #11
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    One would expect that the effect of compressed air released into the barrel and all the othe factors are so small with PCP's that it will hardly have any effect.

    The interesting thing is the fliers are random. If you select your pellets to the same weight and shoot a good grouping and you add a lighter or heavier pellet in between, it results in a fairly random group. My only explanation for this is the barrel movement possibility, how small it may be, it is present.

    I have found with my Walther that I shoot the best group at 792-794 ft/s with a specific brand of pellet. At velocities lower than 770 and higher than 820 the groupings are more than triple in size.
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  12. #12
    Sharp Shooter
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    From my own experience I would say that the main issues are external ballistics and issues with the pellets themselves rather than barrel vibration issues.

    Microscopic variations in the pellet head can translate into real problems, whereas damage to the pellet skirt, unless extreme, does not seem to have a big effect on accuracy.

    Furthermore, while people consider minimum shot to shot velocity variation to be good, this does not automatically translate to accuracy - just goes to show that you should expect the unexpected.

    Dale
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  13. #13
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    Another stone in the bush then and I hope Sniper reads this as well as he can confirm this.

    Walther has a method of tuning the rifle for extreme accuracy with a wide variety of pellets by basically stressing the whole action/ barrel. I have played with this myself a lot to see the extreme changes in group sizes by "tuning" the rifle. Now this is nothing but fine tuning the rifle's mechanical resonance to shoot a good group with virtually any kind of pellet. This test was done with the same batch, same weight, same diameter pellet to eliminate the external effect to a minimum.

    There is a lot of dynamics when shooting and if you add all of these factors together, no matter how minute they may seem to be you will have certain inaccuracies.
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  14. #14
    Protea FT Team '08

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    I cant see that as being a good idea for everyone.Some guys will fiddle and never get a setting that works for them.

    How is it done Francois
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  15. #15
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    Allan. I will show you next time I see you.
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