Gas rifle myth?


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velocette
January 5, 2012, 09:52 AM
Gentlemen;
I have read some accounts about gas operated semi auto rifle accuracy stating that the bolt is moving before the bullet has exited the barrel of the rifle.
Now this sounds a bit far fetched to my practical mind.
Consider:
1, The barrel on my LR 308 is 18" long, the gas block / port is 9" from the muzzle.
2, At the point of the gas port the bullet will be travelling at least 2000 fps or 24000 inches per second. (still acceleration toward the muzzle)
3, The bullet will leave the muzzle in not more than 0.000375 seconds.
4, So, the bled off gas must travel through the gas tube, enter the bolt & build to sufficient pressure to start it moving in LESS than 0.000375 seconds.
5, IMHO, not bloody likely.

Is my math wrong? Or is the idea that the bolt is moving before the bullet leaves the barrel a myth?

Roger

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NOLAEMT
January 5, 2012, 09:58 AM
you are correct, the bolt doesn't move untill the bullet is very much on its way to the target.

Cecil Sharps
January 5, 2012, 09:59 AM
the answer to your question is dependent on the airspeed velocity of an unladen swallow

klcmschlesinger
January 5, 2012, 10:04 AM
And if it can carry a coconut....:p

Rob G
January 5, 2012, 10:15 AM
What type of swallow? African or European?

JustinJ
January 5, 2012, 10:25 AM
The hot gas does have to reach the bolt to move it. It presses on existing air insided the gas tube and compresses it so movement will occur when pressure is at the right level. I'm not saying that the bolt does or does not move before the bullet exits but your math fails to account for this fact.

jerkface11
January 5, 2012, 10:46 AM
Maybe you're thinking of a blowback gun not a gas operated gun?

briansmithwins
January 5, 2012, 10:57 AM
With a blowback or delayed blowback the bolt will start moving before the bullet clears the muzzle.

Recoil and gas operated arms are pretty much invariably set up so that the projectile has cleared the muzzle and bore pressure has dropped before the bolt unlocks.

BSW

JustinJ
January 5, 2012, 11:34 AM
http://en.wikipedia.org/wiki/Blowback_(firearms)

Mp7
January 5, 2012, 11:44 AM
What if the swallow launches from an open dovecote?

(And, are coconuts safe to be reloaded?)

:D

Art Eatman
January 5, 2012, 11:57 AM
Alex, I'll take Post #2 for a closing statement. :D

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