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retired 1
September 22, 2017, 19:51
Been thinking about a 300 BO upper, and all that i see are offered have pistol length gas systems. Is this the norm, and if so, why? I'd think that a full or mid length would be better.
Thanks

84SS
September 22, 2017, 20:19
The gas tube length is either carbine or pistol. Not a high pressure rifle round. More like a pistol round. All powder is consumed in burn of 8-10 inches. If you are going supersonic then you could use a carbine length gas system. Sometimes it can be problematic. If you are going to shoot subsonic suppressed and supers, the pistol gas system will work. Energy and velocity wise. The supersonic 110 grain projectile rounds are close to 8mm Kurz.

idsubgun
September 22, 2017, 21:57
Pistol length is what you want.

I have two, both with pistol length gas systems and both shoot subs and supers without any issues.

Falfan2017
September 23, 2017, 08:49
I had a 7.62x39 pistol that wasn't running right with a carbine tube. Had to drill the gas hole in the barrel substantially larger but it works now. If you run into problems you could try that

HankC
September 23, 2017, 13:14
Carbine length is also common for 16" barrel but mostly for supersonic, may short stroke if subsonic, use light buffer and spring helps. If you intend to shoot subsonic a lot or shorter barrel, go pistol length. On the other hand, pistol length may over gas if 16" barrel/supersonic and folks use adjustable gas block to cut gas down. It is all about what you shoot. Watch for gas port size if carbine length, you want .125" port diameter. I have carbine length 16" barrel and shoot great.

KoKodog
September 23, 2017, 15:25
The gas tube length is either carbine or pistol. Not a high pressure rifle round. More like a pistol round. All powder is consumed in burn of 8-10 inches. If you are going supersonic then you could use a carbine length gas system. Sometimes it can be problematic. If you are going to shoot subsonic suppressed and supers, the pistol gas system will work. Energy and velocity wise. The supersonic 110 grain projectile rounds are close to 8mm Kurz.


yes, pressure is a large part of the equation but not everything


Pistol length is what you want.

I have two, both with pistol length gas systems and both shoot subs and supers without any issues.


yes, pistol length will allow a wide range of different bullet weights and various powders, it allows nearly any decent load to run the action properly



Carbine length is also common for 16" barrel but mostly for supersonic, may short stroke if subsonic, use light buffer and spring helps. If you intend to shoot subsonic a lot or shorter barrel, go pistol length. On the other hand, pistol length may over gas if 16" barrel/supersonic and folks use adjustable gas block to cut gas down. It is all about what you shoot. Watch for gas port size if carbine length, you want .125" port diameter. I have carbine length 16" barrel and shoot great.


carbine length does not allow enough dwell time for a wide range of loads, even opening up the gas port will not always allow proper function, that is why nearly everyone has switched to pistol length

retired 1
September 24, 2017, 23:53
Thanks for the replies. I'm not that familiar with ARs, and it didn't seem right to use the pistol length. Now I know the reasons.
Thank you every one for the education.

MistWolf
September 28, 2017, 20:24
The 300 BLK works best with a pistol length gas system, not because it's a low pressure round, not because of dwell time, but because the 300 BLK uses less powder which generates less gas that has to fill the greater volume of a larger bore

gentlemanjoe
September 28, 2017, 21:16
Pistol length will allow a wide range of different bullet weights and various powders, it allows nearly any decent load to run the action properly

Short and sweet.:|