AR Barrel Q's

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Oct 28, 2005
Doing another build, and I found an interesting barrel on CMMG. It is a 16" barrel that has the gas port drilled at the rifle length position.

Are there any advantages to this vs a midlength? Reliability? Velocity? Accuracy? etc. (when comparing to others in the 16" flavor)

The goal in mind will be the epitome of all that is black rifle. I already have a couple of KISS rifles so, this will be just a toy. I want to do Gecko45 proud.

It will be mounted on this upper in rifle length:

I am also looking at building a pistol with a 7" barrel using their carbine upper if I like it.

Anyone use one of these uppers? Feedback on them is kinda nill.

Any and all input is appreciated.

i have a 17" barrel with rifle-length gas and it works awesome.
i have no experience personally with 16", but from what i've read, i think that's too short unless as highorder implied, they've done something else to compensate. still, i didn't think the issue was volume of gas but rather how long it's under pressure
I'd tend to go mid lenght on a 16 inch barrel. I've heard the rifle length on 16's might have some reliabity issues.

If you want rifle length sights, CMMG does offer one 16 inches, midlength gas, and rifle length sigts. I'd be more comfortable with this type of arrangement for reliability.
Why not contact CMMG and ask?

The Dissipator style 16" barrels are nice for the additional sight radius. CMMG sells them with CAR, Midlength, and rifle-length gas systems.
I think the vis is a waste of money for your purposes and a rifle length gas system on a 16" barrel is probably a step in the wrong direction reliability wise.
Anyone use one of these uppers?

I'm using one with a Noveske 18" barrel. It is a nice upper. I got mine for relatively cheap, but if I hadn't I'd probably just go with some rails from Larue or DD, depending on the price.

If you were going to use the barrel changing feature (I don't plan on it) that might be a plus, or if you really need a super sturdy rail perfectly in line with your upper receiver (I don't know why, perhaps a night vision setup?) then the VIS is probably top notch. I have an ACOG on mine, and little else. As I said I'm happy with it, but I wouldn't pay a premium to have it over the usual rail system.

Agreeing with others, I've always heard that 17" was the low number for a rifle length system, but CMMG knows more about ARs than I do, so maybe they have good reason.
The issue is, is there enough gas/pressure passed through the port between the time the bullet passed the port and leaves the barrel.

I'm not sure that it's doable w/o a suppressor.

Also, are you sure the port's there and just not the shoulder for the sight base? Some barrels have a CAR gar port and another "shoulder" or whatever at the location for a rifle for your sight base only.
OK we will stick with the middy (reliability reasons).

Not to worried about sight radius (I will use a handguard flip) Might put a low profile gas block on it with a rifle length VIS. Shroud the barrel. (that thing that goes up)

The reason for the VIS is its the cheapest monolithic upper that I know of strictly for "cool" factor. Laser sights to sight in my laser sights kinda thing.

I'm thinking Magpul CTR, rail covers Pmags w/ ranger plates. All in flat dark earth.

I already have SHTF etc. This one is for fun.

This is strictly a range toy. But needs to function.
Doesn't seem like there would be much dwell time on a 16" with a rifle-gas system. Perhaps the gas port is drilled to a larger diameter to make up for the shorter dwell time? Who knows?

Mid-length on a 16" is a very good idea. The 16" with CAR system (same as M4 for 14.5" barrels) is over-gassed. It has all the pressure of the 14.5", but extra dwell time due to the longer barrel. 16" CAR is perhaps the worst of the common barrel/gas-system combos.

Midlength still not as good as rifle system, but an improvement. Whatever the case may be, you want a system that will work with a wide variety of ammo. Some of these nonstandard and uncommon varieties may work great with hot ammo, but not so well with a lighter load or the opposite. That's a no-go. No matter what the purpose of a firearm is, the main purpose should be that it functions well.
Good info in this thread. A 16" with rifle length gas system has a very short dwell time and has a number of issues similar to the 10.5" shorties with a CAR gas system. It doesn't mean they won't run or can't be made to run; but they often have more problems than a midlength or carbine - particularly as it gets colder.

MSTN does 17" rifle length gas that run like a top and that is the shortest I would personally go if trying to use a rifle length gas system.
Hi Guys-

I just got a 16" CMMG rifle with the rifle-length gas. After 100 rounds of WWB and 300 rounds light reloads, no cycling problems yet.


A guy on with a CMMG M10R removed his FSB and measured the gas port. It is .110" which is consider optimal for that configuration of barrel length and gas port location by most of the people who do the conversions.
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