Mid Gas system on a Carbine

Red Belly

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I have a carbine AR15 (5.56) with collapsable stock. I am running it with an H buffer and FA BCG.

I want to build a MK12 type precision upper,18" barrel etc to run on my carbine lower.

My question is what is the recommended set up for this? Right now I am leaning toward mid length gas system & FA BCG. I think a rifle length gas system may give me some issues.

Thanks for the help.
 

TP4

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Re: Mid Gas system on a Carbine

I run mid-length gas systems on my 16" and 18" builds.
 

Red Belly

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Re: Mid Gas system on a Carbine

I am looking at a WOA barrel. The 2 choices are either rifle or mid length gas system.
 

Dtarget

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Re: Mid Gas system on a Carbine

I would go for the rifle length gas system. If you plan to use a fixed front sigh, the longer sight radius is a plus. 18" barrel with rifle gas is a fairly common set up. Doesn't the real Mk12 use an 18" barrel with rifle gas?
 

-=boone=-

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Re: Mid Gas system on a Carbine

WOA 18" SPR MID

ar001.jpg
 

-=boone=-

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Re: Mid Gas system on a Carbine

It runs well. It would probably run better with an actual AR15 shooter behind it. It has been a constant learning curve for me. I've shot golf balls at 400 with it.

I'm still testing ammunition at this point. 5 shot groups.

75 Grain HSM Match has been the winner so far. Solid ¾ Moa groups with some ½ moa groups.

I still have to order the 77 Grain HSM to test.

77 Grain Black Hills re-manufactured match Is absolute shit out of my rifle. 1.5 -2 Moa or larger groups. That really blows when you purchase 200 rounds of it. If you don't reload test ammo in smaller quantities.

XM193 55 Grain shot gun patterns. 3 Moa or greater.

PMC 55 Grain, 1-1.5 moa groups. I can order 1000 rounds of this for $300.
 

Red Belly

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Re: Mid Gas system on a Carbine

I will be hand loading for it. Thanks for the info.
 

uscbigdawg

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Re: Mid Gas system on a Carbine

On an 18" barrel, go rifle length gas. Smoother gas impulse and in my opinion, inherently more reliable.

Rich
 

carbinero

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Re: Mid Gas system on a Carbine

Since it's custom made, with the correct gas port diameter, you shouldn't have a problem. Issues sometimes occur when people cut down a 20" to an 18" without taking that into account. So given those choices, I'd also go rifle.
 

splean

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Re: Mid Gas system on a Carbine

Unless you really want the look of a covered gas block I would suggest the rifle length gas system for the aforementioned reasons. Good luck.
 

Michaelvoigt1

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Re: Mid Gas system on a Carbine

Having had both the mid and rifle length systems on 18" barrels, I would definitely go with a rifle length gas system on a new 18" build.

You will have lower gas pressure operating the bolt carrier, resulting in a smoother recoil impulse. You have plenty of barrel in front of the gas hole to provid\e a proper gas dwell time.

I have not seen any advantage running a shorter than necessary gas system. They are always found a shorter gas sytem sharper in recoil and more prone to tearing up brass due to quick opening (some times resulting in malfunctions from filling the ejector hole with shavings).

MV
 

Red Belly

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Re: Mid Gas system on a Carbine

Thanks gents. I think I have decided on the rifle system. I just read an article from a good friend about gas port location etc. It pretty much summed up what you guys have been saying.

Thanks again & happy new year to all.