18; Mid vs Rifle gas system

[jeffy]

I've been looking at getting another upper to go alone with my 14.5. Now I've noticed that many of the companies out there that make an 18" barrel seem to prefer the mid-length gas system. I would have thought a rifle gas system would be better. I'm sure I'm missing something.

I'm also thinking about building this one myself. The lower was too easy and slapping on the upper was kind of like cheating.

[Paulo_Santos]

The Rifle length system is softer shooting, but it can sometimes have short strokin issues with some weak ammo. You need a certain barrel length past the gas port in order for the AR to cycle properly without having to open up the gas port too much. Noveski actually uses what is called an Intermediate gas port which appears to be ideal for the 18" barrels.

[TigerStripe]

Jim Sullivan, one of the other engineers who worked with Stoner to create the AR15, says seven inches from the gas port to the end of the barrel is the optimal distance.


TS

[jeffy]

So then, this brings up the question. Why does the SPR uses the rifle-length gas system?

[docsherm]

Jim Sullivan, one of the other engineers who worked with Stoner to create the AR15, says seven inches from the gas port to the end of the barrel is the optimal distance.


TS

Seven inches???? That doesn't make any scene. Then why did they make the original AR15 with a gas block 6" form the end of a 20" barrel?

[TigerStripe]

Seven inches???? That doesn't make any scene. Then why did they make the original AR15 with a gas block 6" form the end of a 20" barrel?

It's 6.875" from gas port to the end of the bore. With the edition of a three-prong, A1 or A2 flash suppressor that's just a little over 7".



TS

[docsherm]

OK, so the flash hider is included. That makes scene. Thanks for the info.

[jeffy]

OK, so with the Ops Inc MK12 SPR brake being 6.25", it gives an SPR 7" and change?

So then if one was to use a AAC/Vortex or an A2, it would be better to go with a mid-length system. OK, I think I understand now.

[TigerStripe]

The info I'm using is from the May 2008 issue of SAR, which has the Masada on the cover. It's on page 54. Quoting Jim Sullivan,

On the M4 carbine, like the original rifle, it's about seven inches of travel (from gas port to muzzle). You need to maintain that distance when you make a carbine and they did that on the M4.

TS

[gotm4]

So then, this brings up the question. Why does the SPR uses the rifle-length gas system?

The MK12 is shot 99.9% of the time with a suppressor mounted. Rifle length with the use of a suppressor is best.