GTA
All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Topic started by: bountybuddy on March 26, 2017, 01:21:58 PM
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Please answer these two questions if you can. I hope to buy the new FX Crown and plan on shooting both the .177 and .22 in it. Thank you so much for your help. Shoot safe.
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Bud,
It's really going to depend on the pellets you will be shooting. Usually pellets at the heavier end of the range will need a faster twist rate.
There is this twist rate calculator that you can use to get an idea:
http://www.geoffrey-kolbe.com/barrel_twist.htm (http://www.geoffrey-kolbe.com/barrel_twist.htm)
It's the only calculator that will model subsonic projectiles that I know of.
I had started a similar quest here:
http://www.gatewaytoairguns.org/GTA/index.php?topic=115934.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=115934.0)
concerning H&N Piledriver pellets.
Thanks,
Taso
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I can't recall specifics, but I remember a thread a while back concerning twist rates also looked at velocity.
Since your interest is in an FX gun, that means a smooth-twist barrel, which means you're probably not going to have much say in the matter, as much of the anecdotal reading points to their barrels being designed for working with JSB pellets.
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Peter,
I think I heard in a video review of the FX Crown that it will have interchangeable barrels in different twist rates and in smooth twist and standard twist?
The Kolbe calculator does account for pellet velocity too. You can see sample graphs at the end of my thread.
Thanks,
Taso
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Gees, I don't have a clue. I hope the airgun manufacturers do.
I know that the longer the projectile, the faster the twist needs to be.
And the faster you can push a projectile, the less twist it needs.
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Please answer these two questions if you can. I hope to buy the new FX Crown and plan on shooting both the .177 and .22 in it. Thank you so much for your help. Shoot safe.
I don't know that I'd be overly concerned. If you're using diabolo pellets, then they are pretty forgiving with the twist rate.
Some examples of such...
There are airgun barrels ranging in twist from 1:16 to 1:26 and they all do well at stabilizing the pellets, and a variety of pellets as well
Pellets from the same twist rate can be stable from 350 to 950 fps
Twist rates at the muzzle can be less than half the twist rate at the target (velocity decays much faster than angular momentum)
So, the actual rpm can vary, the rpm per fps can vary, and both will vary during the ballistic flight. The distance you shoot is another variable. Use a lower or higher powered gun, use a different twist rate barrel, or do both and you have a wide range of examples that generally still work. Hope that makes sense. Slugs and bullets are a different matter.
Wyo