Full Auto Bolt Carrier Assembly for AR-15


June 20, 2007, 01:45 AM
What are the advantages of this?

Is it better quality than semi carrier?

Is it worth the extra money?

Can this be put into Stag 2H upper AR-15?

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June 20, 2007, 01:49 AM
You may run into some daft legal issues having FA parts in an AR.

Don't Tread On Me
June 20, 2007, 02:05 AM
What are the advantages of this?

It is the correct weight for a carrier. It also has a shrouded firing pin. That is the original and correct design. AR-15 carriers are specifically designed to jam if there is a disconnector failure. Designed to JAM. An M16 carrier will just slam-fire and dump the whole magazine. If my life depends on it, I'd rather deal with a full auto AR than be a corpse with a hammer/firing pin jammed AR. Even then, there is no proof there was "intent" to manufacture a full-auto. A broken disconnector is far from deliberately manufacturing or modifying a rifle to be fully automatic.

Is it better quality than semi carrier?

Hard to say for sure since some commerical AR-15 carriers are good quality. But it is safe to say that most M16 carriers are made by companies that have miltiary contracts. Such as Colt, CMT, LMT. These are widely held to be of higher quality. Such parts are made to specifications and tested for quality. I'd give the edge to the M16 carriers.

Is it worth the extra money?

For me, absolutely. It isn't that much more expensive. Bravo Co. has CMT and LMT M16 carriers for $130. They are also MPI tested. Hoplite had Colt M16 carriers for $180.

Can this be put into Stag 2H upper AR-15?

It can be put into ANY standard AR-15 that is chambered in .223/5.56

You may run into some daft legal issues having FA parts in an AR.

See the BATFE letter to Colt discussing this very issue. I'm sure someone will come along and post the JPG of it. It is legal. M16 carrier does not make the rifle full auto.

Of course, this is the internet. So believe what you want.

June 20, 2007, 02:14 AM
Colt has been been shipping NEW semi-AR's WITH the auto carrier installed. No legal worries..enjoy!

Gary G23
June 20, 2007, 08:29 AM
I would not get an AR without a FA carrier.

June 20, 2007, 11:04 AM
I would not get an AR without a FA carrier.
I concur. The BCG is a critical component that can be the deciding factor in having a POS or an uber-reliable weapon. Do not skimp or pinch pennies when buying the bolt+carrier.

High Planes Drifter
June 20, 2007, 11:26 AM
This is great info; Im in the process of a build as we speak, and had absolutely NO IDEA there was a difference. Great info ! For the little bit of extra money, I will certainly go with the M16 carrier group

June 20, 2007, 11:31 AM
Personally I think the FA bolt carrier works so well be cause the extra weight seats the rounds more positively.

Zak Smith
June 20, 2007, 11:52 AM
Changing reciprocating mass in an AR-15 has several effects which should be understood before making changes to the system.

Here are some comments I wrote for someone else a while ago:

There are a bunch of variables that affect the system, and reciprocating mass is one of them. Magazine spring strength, gas port location and size, bolt carrier group being in spec or not, etc , all play into the system and make the AR-15/M4 work or not work.

There are several physical facts to consider:

1 with everything else the same, more gas pressure will cause the BCG to cycle faster

2 with everything else the same, the shorter the gas system, the higher chamber pressure will be when extraction starts

3 with everything else the same, the more reciprocating mass, the longer extraction from #2 will be delayed

4 weak mag springs cause the rounds to rise slower, and are a leading cause of AR-15 malfunctions when the bolt cycles faster than the top round can rise. this failure mode can be reduced by making the bolt carrier group take less time to get back to that portion of the return stroke

5 everything else the same, the more reciprocating mass in the system, the longer the action will take to cycle

6 everything else the same, the longer mass is in motion the more delay until the gun is ready to fire again (and the sight picture stops moving from inertia events)

There are competing theories on what "reduces recoil" the most. I, and just about all competitive 3-Gun / practical rifle shooters, have concluded that less mass produces less sight picture movement and the gun is back on target and ready to fire again sooner. Take that for what it's worth.

Facts #2 and #3 above contribute to the reliability problems in the M4 (and carbine-gas 16"-ers) that caused the SOPMOD/M4 improvement project some years ago. This effort yielded some changes in extractor setup, some bolt improvements, and I think some changes in buffer.

The issues are also covered in this ArmaLite tech note:


I avoid the M4 gas system (carbine gas) if I can. It has too much gas pressure and the chamber pressure has not dropped enough by the time the bolt starts to unlock. This contributes to reduced reliability and reduces parts lifetime. That said, my 12" SBR has the carbine/M4 gas system and it runs 100% (Noveske upper). I run a regular carbine buffer in this, but a M16 bolt carrier which is a little heavier than a regular AR-15 BC (and it's what was shipped with the upper).

The midlength is a better choice if it can work with your barrel. I run either stock AR-15 or slightly lighter bolt carriers in these and a regular carbine buffer.

With a rifle-length gas system, I again run a regular carbine buffer but then a slightly lightened bolt carrier.

My summary comment is to start with a good factory upper and then don't mess with it unless something doesn't work, in which case it's probably better to send it back to the factory.

January 13, 2011, 05:47 PM
I was wondering this same thing the OP asked. I found this thread via search and I am wondering if this is the final word on this as I just bought a complete m16 bcg from bravo company. It seems everyone here says it is a good idea with the exception of the one poster. Anyone else care to chime in? Anyone running an m16 bolt carrier group in their AR 15? THANKS!!!

Jon Coppenbarger
January 13, 2011, 06:22 PM
It has been a common practice for some highpower competition shooters to use them. The tubb carrier weight system was designed from my belief to allow a slightly longer dwell time in the cycling rate to allow slightly hotter loads or to help reduce pressure signs.

Some rifles have problems if you have wear on your gas tube and use them. The original style carrier and its heavier weight is believed to act the same way. In run and gun events with a mag resticted round and lighter bullet (55,62, ect) it should work as well as not having a heavier carrier. But now when you start using a vld or even say 80 to 90 grain rounds in your ar15 style of weapon alot of folks are using them. Some people swear by them for rapids and it really does slow it down slightly.

January 13, 2011, 06:44 PM
Here is a good question too.....Would it be a good idea to change the buffer? Maybe an H buffer? Is the buffer and spring different for the commercial tube vs the mil spec tube??? Thanks.

January 13, 2011, 06:58 PM
You should have an H buffer anyway.

Use the heaviest buffer your weapon will function with.

January 13, 2011, 08:24 PM
As mentioned previously, the Tubb Carrier Weight System used with a carbine gas system does help with a bunch of problems from sooty brass to extraction issues.

January 13, 2011, 08:51 PM
Top semiauto carrier, unshrouded firing pin tunnel
Middle, semiauto carrier, shrouded firing pin tunnel.
Bottom, fullauto carrier, heavier rear tunnel, full shroud firing pin tunnel.
Top, semiauto carrier, unshrouded firing pin tunnel.
Middle, Fullauto carrier.
bottom, semiauto carrier,shrouded firing pin tunnel.

If you choose to incorporate a Match trigger/hammer assembly in your rifle, I strongly recommend you choose a carrier with a shrouded firing pin tunnel as the thinner hammers used in match assemblies can catch and hang up in the unshrouded firing pin tunnel carriers.

Heavier carriers used in conjunction with slightly heavier buffers in carbine length rifles tend to reduce snappy bolt cycle which helps keep the rifle on target for repeat shots, this can speed up your time in competition shooting.HTH

Jon Coppenbarger
January 13, 2011, 09:04 PM
But remember some of us are talking two different sports with reguards to what we wish the weapon to do. Rapid fire in highpower is a timed event which you will fire 10 rounds with a mag change in either 60 seconds at 200 yards in a sitting position and 70 seconds in a prone position from 300 yards. The ideal is to shoot a clean 100 score which is not uncommon to do for advanced shooters. Now in this type of sport you should take a breath between shots so the extra time it takes for recoil is there.
I have never used the tubb system but do love the extra weight of the carrier in what they call rattle battle matches. That is timed fire in 50 seconds starting from 600 yards on a shillouette target. 25 hits and up out of a 30 round mag are common with the right wind call. check it out on you tube and you will see some good shooting. and I find that good enough to protect myself. have seen some of the good military shooters in this match shoot close to and up to TWO mags of 20 rounds with the mag change with high hit total in that 50 seconds.

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