GTA
All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Topic started by: Aldo on June 16, 2012, 01:37:28 AM
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why would I have to adjust my scope left and right when changing pellets?......I can understand up and down.....but right left????.....does the pellet corkscrew when in flight???
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Corkscrew ...... yes indeed many pellets do !!
Change range far enough POI may indeed shift sides or go up/down from your baseline range :P
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Heavier pellets are less effected by cross wind. I had to change my windage turret by a few clicks when switching from a JSB 15.89gr to an H&N 14.66gr. I've noticed that the head shape has some effect on the amount of windage drift, too.
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dont think its windage shooting at only 20 yards not windy
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Regardless of wind. Different pellets will sometimes have different points of impact.
It is normal.
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if the pellets weight is out of balance, like for example ur car tires if you drop the psi in one tire down to 20pds and take a spin. bet once you 45-60 mph ur going to start feeling that infamous out of balance tire feeling. so a pellet out of balance is not going to spin like it should, its spin will start to wobble. pellets from 2 different brands and both being domed are going to have a different spinning balance.. i guess thats how i would word it
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I've been thinking about these shifts in poi for a while. I'm thinking that rather than being the weight or shape that is actually causing the POI shift, it is the change in the harmonics of the barrel that is the culprit. As the weight of the pellet changes, so does the moment it actually leaves the muzzle. If the barrel is vibrating the POI will be determined by the position of the barrel at the moment of release. The same effect will be observed if the pellets are inconsistently sized as there will be a change in the speed of the pellet giving a corresponding change in the moment the pellet leaves the barrel(therefore a POI shift). Think of it this way... when a barrel is vibrating on an axis, there is a point at the center of the "wave" where the release of the pellet is uniformly affected by the motion of the barrel. As the normal point of release moves further from center, any change in that moment will have a less apparent effect on the POI. This is due to the fact that the motion of the barrel is fastest at the middle of the "stroke" and will be slower as the motion gets to each end of the stroke as the barrel will be resisting the motion in order to return in the other direction. I think a similar change to the moment of release can be realized when changing the length of the barrel. My thought is that any springer that releases its pellet at or near the end of its stroke will be more consistently accurate. The POI will be furthest from the centerline of the barrel, but subtle changes in velocity will affect the POI least as there is less movement of the barrel at that point. The offset can be nullified by adjusting the sights.
Nothing scientific about my thoughts other than some applied logic, at some point, I'll do some testing by changing barrel lengths in small increments to see if any of this holds up and can be repeated to get maximum consistency (acccuracy)with various barrels. I'd welcome input from some of our "AG-Techno-Geeks" who may have thoughts on this.
pv
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....I'm thinking that rather than being the weight or shape that is actually causing the POI shift, it is the change in the harmonics of the barrel that is the culprit.
I agree with this. When I change pellets I can feel and hear the rifle change its firing characteristics. It often takes 5+ shots to get it to group, and the POI is different than with the previous pellet. This happens even indoor at 10 yards - so no wind issues. I found this more so for springers but also for CO2 and PCP - barrel vibration harmonics and interaction with lock time (when pellet exits muzzle) all happening to affect POI.
Conclusion, pick a pellet and stick with it - I have a spreadsheet with each rifle listed.
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It's the same with P.Bs. Some say barrel mating, barrel movement, weight, etc. etc. I too get 1 and stick with it. The exception (for me in a CFX), is the Crow Mags, which I really like. But if you shoot them, you can pretty much figure the difference, and really don't need to do a bunch of adjusting, (for me, it's a 12:00 hold, versus 6:00), since they're not meant for much more than 20-25 yards. Of course, some guns hate 'em.
Good Luck to Ya! Mike
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i don't know much about internal ballistics (at least, not with airguns) but i strongly suspect that Paulie has it right.
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wow... physics at work ...still searching for the right pellet for my gun......been shooting JSBs with ok results.....friend got a can of Superdomes that worked better in his gun so I had to try um....barrel vibration....really?
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They really do watch this. ;D
http://www.youtube.com/watch?v=FaW_Hs0B79c# (http://www.youtube.com/watch?v=FaW_Hs0B79c#)
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If you change your shooting style it can also influence the shot. ;D
http://www.youtube.com/watch?v=OYm_tI7mbBw#ws (http://www.youtube.com/watch?v=OYm_tI7mbBw#ws)
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They really do watch this. ;D
http://www.youtube.com/watch?v=FaW_Hs0B79c# (http://www.youtube.com/watch?v=FaW_Hs0B79c#)
Indeed they flex !! .... Wow really shows how much.
Just an FYI, last year after doing a rebuild on the FWB 124 did a custom full length shroud that substantially stiffened the barrel assembly .... results were an even MORE accurate rifle !!
So even tho a shroud may be just So So in noise reduction, stiffness and vibration reduction during the shot has made it WELL worth it.
JMO ...
Scott
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And all this time I thought I was having an epiphany! :o Guess I'll just have to settle for a better way to control it!
pv
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http://www.arld1.com/holdingspringers.html (http://www.arld1.com/holdingspringers.html)
http://www.google.ca/url?sa=t&rct=j&q=air%20rifle%20links%20and%20demos&source=web&cd=1&sqi=2&ved=0CFwQFjAA&url=http%3A%2F%2Fwww.arld1.com%2F&ei=-xjeT-ekDILa6gHI0ayhCw&usg=AFQjCNGImkfkXRsq_ZrMHgWiPsBHjWzq2g (http://www.google.ca/url?sa=t&rct=j&q=air%20rifle%20links%20and%20demos&source=web&cd=1&sqi=2&ved=0CFwQFjAA&url=http%3A%2F%2Fwww.arld1.com%2F&ei=-xjeT-ekDILa6gHI0ayhCw&usg=AFQjCNGImkfkXRsq_ZrMHgWiPsBHjWzq2g)
I found this along with other links.
Hope these help a bit.
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that's pretty neat, Kid.
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Aldo, sometimes you can see the corkscrew if you get a little longer range and the sun behind you....s10gto cool video.... 8)
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Could be why Air Arms springers have short shrouded barrels. Good info.
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Great stuff, Rob! We need to get this or a link in the library, really valuable info for newbies and a refresher for the rest of us!
pv
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uncle paulie nailed it!
And he needs to acquire one of the harmonics altering barrel brakes once made by Vortek. (they may still do so)
I got one on an R-1 I bought from a friend many years ago. It uses a weight which screws in or out on very fine threads to alter the barrel harmonics. The effect such minimal movement has boggles the mind!
It is possible to 'walk' the POI all around the target with tiny adjustments.
Using it extensively constitutes a virtual graduate degree program on the effect of harmonics on springer accuracy! Tom
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uncle paulie nailed it!
And he needs to acquire one of the harmonics altering barrel brakes once made by Vortek. (they may still do so)
I got one on an R-1 I bought from a friend many years ago. It uses a weight which screws in or out on very fine threads to alter the barrel harmonics. The effect such minimal movement has boggles the mind!
It is possible to 'walk' the POI all around the target with tiny adjustments.
Using it extensively constitutes a virtual graduate degree program on the effect of harmonics on springer accuracy! Tom
interesting. anyone familiar with Browning's BOSS system? similar concept.
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dang guys....tanks for da skoolin.....even and old dog....bla bla bla
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I had a similar problem with different pellets, especially different weights. I determined my issue was more from torquing than harmonics. See this thread. http://www.gatewaytoairguns.org/GTA/index.php/topic,27294.msg248704.html#msg248704 (http://www.gatewaytoairguns.org/GTA/index.php/topic,27294.msg248704.html#msg248704)
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Thanks for this post, I would shoot 3 different manufactures and maybe a couple different types by the same in an evening and spend a lot of time adjusting and blaming my scope.
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good luck
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if you think something shoudl be a sticky, gene or dave (ezman604) would be the people to speak. id prolly pm gene first on this one..
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Huh?
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Oh....now I get it...you guys have been a big help...I have been trying alot of diff pellets and doing more scope adjusting than shooting....well Ill just pick one pellet and stick with it....for me its the JSB exact 8.4s
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I had thought about something attached to the barrel similar to the weight-balls they put on long high tension wires to keep them from establishing a wave motion(bridge cables also) but I think i would rather opt for a cleaner "look" by changing the length(frequency) instead. The biggest problem I have with all of this is that we're on the low end of the scale and anyway you look at it, it's likely going to vary from barrel to barrel just as most everything we do to these things because the kind of precision we desire is just not built into the products at these price-points. I think the situation is better once you get in the $ 1000+ price range, but those aren't perfect either.
pv
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my old gamo whisper and gami bigcat both liked having a bipod on the barrel and shooting off the bipod. just slide it down an inch or so and test the grouping... i never had any problems cocking them and i had the bipod on both mounted about 3inchs forward of the breech block, just enough room to allow it to cock properly..
uts makes a nice clamp on barrel bipod with folding legs that extend 9 to 13 inches.. its a great bipod and ive owned 2 in my springer days
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The biggest problem I have with all of this is that we're on the low end of the scale and anyway you look at it, it's likely going to vary from barrel to barrel just as most everything we do to these things because the kind of precision we desire is just not built into the products at these price-points. I think the situation is better once you get in the $ 1000+ price range, but those aren't perfect either.
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The goal is reducing variables.
Even if all is right with the gun you're still subject to ammo variations.
I look for a pellet that enters the leade with the same pressure required each time. If you can feel a wide variation of pressure to seat the same pellets from the same box (like the infamous CPHP) there's little point in pursuing it further. Because of 'stiction' the pellets are going to start their journey to the muzzle at different times---and leave it at a different point in the harmonic cycle.
A perfectly balanced system of shooter, gun and ammo is the ever receding goal. Tom