Thread: Rifling
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Old 02-05-2013, 06:58 PM   #31 (permalink)
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Join Date: Oct 2006
Location: Bowie MD

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Originally Posted by Spider! View Post
A few of thoughts to add;

On an over-bored barrel the round should at least be bumping into the sides as it goes down the bore. If not, I would use that barrel anyway. When it bumps, it will be bumped to twist with the rifling. I don't see how you would not get some rotation.

Any rotation from the barrel is a jump start and should be a good thing if the round can stand it. Too much rotation (more than the angle of the fins) should be wasted unless you have a muzzle condition, which is next...
Thie issue is the material's shear strength is very low, so when it bumps into the rifling, it is more likely to shear off the polystyrene than it is to impart spin. (This is of course my opinion, not backed with facts.)

Originally Posted by Spider! View Post
Porting and barrel length should matter (if any of this does). On a short bull barrel (no porting) the gas escapes forward of the round, which should at least delay the establishment of air flow over the fins, if not push them the other way. With the right amount of porting and barrel length, the round can exit with little or no blow-by.

Yes? Da? Si? o no?
Yes, and I had not thought about the porting/bull barrel... I think we need to send some barrels to Punkworks, as they has access to a high frame rate camera. We should be able to see the difference in spin up times if the porting does what you theorize it will.


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Last edited by tymcneer; 02-05-2013 at 07:08 PM. Reason: Had a DUH moment
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