Gemtech introducing suppressed bolt carrier

[themonk]

Personally I think it's a great option for those that dont want to a have an adjustable gas block on a fighting rifle. It is also a tool less change as the carrier can be adjusted with just a case.

[punkey71]

I prefer an adjustable gas block and an LMT enhanced carrier with enhanced cam pin track, with the A5H4 buffer over an adjustable carrier for the simple fact that an adjustable carrier is using the gas tube as a pressure vessel in a manner that hasn't been explored much from an engineering standpoint.

Throw in a tubbs AR10 flat wire spring and you have my setup with zero gas to face and minimal exiting the ejection port even with full NATO pressure ammo.

I'm sure the SBC is a quality unit, and it may be the only option for some. But it's not my first recommendation.

Buford, can you expand on your concerns regarding gas tube pressure?

[Ned Christiansen]

[BufordTJustice]

Buford, can you expand on your concerns regarding gas tube pressure?

Sure, my concerns are pretty simple. The AR system won't allow the bolt to unlock until there is enough gas pressure to act against the stationary piston to move the carrier rearward. This pressure is applied via expanding gas in the expansion chamber, which is the rough shape of a toroid (donut) around the tail of the bolt.

A regulated bolt carrier puts the artificial bottleneck for the gas at the gas key. This means that additional pressure is maintained inside the gas tube, longer.

An adjustable gas block puts this overpressure in a tiny chamber between the much-stronger gas block and the gas block journal on the barrel.

Anybody who is "worried" about putting a fancy thing like an AGB on their fighting rifle ought to think about that as well.

I might also add that Black River Tactical's FSB/Lo Pro gas block inserts are another caveman simple option. I just don't like the idea of putting an unknown in the weakest part of the gas system; the gas tube.

With that said, Gemtech is a solid company that makes quality products and i don't doubt that people are getting positive results with them. It's just not my preferred method of gas regulation. And nothing but a highly in depth technical and engineering analysis is going to change my mind on that.... though i am certainly willing to consider that kind of data if it becomes available.

EDIT: to be clear, I'm not saying it's a bad option. It's just not my preferred option.

[BufordTJustice]

Personally I think it's a great option for those that dont want to a have an adjustable gas block on a fighting rifle. It is also a tool less change as the carrier can be adjusted with just a case.

Indeed. For some, it may be the only option.

[klawson]

Sure, my concerns are pretty simple. The AR system won't allow the bolt to unlock until there is enough gas pressure to act against the stationary piston to move the carrier rearward. This pressure is applied via expanding gas in the expansion chamber, which is the rough shape of a toroid (donut) around the tail of the bolt.

A regulated bolt carrier puts the artificial bottleneck for the gas at the gas key. This means that additional pressure is maintained inside the gas tube, longer.

An adjustable gas block puts this overpressure in a tiny chamber between the much-stronger gas block and the gas block journal on the barrel.

Anybody who is "worried" about putting a fancy thing like an AGB on their fighting rifle ought to think about that as well.

I might also add that Black River Tactical's FSB/Lo Pro gas block inserts are another caveman simple option. I just don't like the idea of putting an unknown in the weakest part of the gas system; the gas tube.

With that said, Gemtech is a solid company that makes quality products and i don't doubt that people are getting positive results with them. It's just not my preferred method of gas regulation. And nothing but a highly in depth technical and engineering analysis is going to change my mind on that.... though i am certainly willing to consider that kind of data if it becomes available.

EDIT: to be clear, I'm not saying it's a bad option. It's just not my preferred option.

Maybe I'm mistaken, but doesn't the SBC work just like every other carrier on the unsuppressed setting, with the same amount of gas, then when turned to suppressed it opens an additional port on the carrier, tentatively reducing the pressure even more. If so then this has no effect on pressure in the gas tube.

Again, maybe I'm mistaken but that was my understanding of how it worked to regulate pressure.

[JoshNC]

Is that hole present to allow adjustment between suppressed and unsuppressed without bolt removal?

[Benito]

I agree with an adjustable gas block being more effective due to finer adjustments. Cost could be argued depending on your situation.

-multiple rifles that need adjustable gas blocks vs. 1 SBC
-rifles with 45 degree, press fit gas blocks (i.e. LMT MRP barrels).
-having to mail your barrel out for an AGB install (I have no local gun smiths I would personally trust).


The only adjustable gas block I personally am interested in is the Micro MOA. That is around $125 IIRC. A SBC is around $180 (if you already have a bolt to use). For me, it is cheaper, and makes a lot more sense to use a SBC.

Those are good considerations that I didn't think of.
I like to have rifles that are complete, though. No way would I want to have to have to borrow parts from one rifle to make another functional.

I'd usually agree but some people have multiple SBR's(Or uppers) and rather than getting an AGB for each, the carrier doesn't seem like a bad thing.

One AGB = less than 1/2 the cost of one SBC. Plus you then have to swap out bolts (unless one is also sharing bolts between uppers). A good AGB makes more sense to me based on the cost and simpler logistics.

Whoa. Interesting modification and very cool idea with the chart on the side.

Sure, my concerns are pretty simple. The AR system won't allow the bolt to unlock until there is enough gas pressure to act against the stationary piston to move the carrier rearward. This pressure is applied via expanding gas in the expansion chamber, which is the rough shape of a toroid (donut) around the tail of the bolt.

A regulated bolt carrier puts the artificial bottleneck for the gas at the gas key. This means that additional pressure is maintained inside the gas tube, longer.

An adjustable gas block puts this overpressure in a tiny chamber between the much-stronger gas block and the gas block journal on the barrel.

Anybody who is "worried" about putting a fancy thing like an AGB on their fighting rifle ought to think about that as well.

I might also add that Black River Tactical's FSB/Lo Pro gas block inserts are another caveman simple option. I just don't like the idea of putting an unknown in the weakest part of the gas system; the gas tube.

With that said, Gemtech is a solid company that makes quality products and i don't doubt that people are getting positive results with them. It's just not my preferred method of gas regulation. And nothing but a highly in depth technical and engineering analysis is going to change my mind on that.... though i am certainly willing to consider that kind of data if it becomes available.

EDIT: to be clear, I'm not saying it's a bad option. It's just not my preferred option.

Never thought about that. A ruptured gas tube would suck pretty bad.

Is that hole present to allow adjustment between suppressed and unsuppressed without bolt removal?

I think that's the idea. That guy must REALLY like that SBC to modify his upper like that.

[Ned Christiansen]

Yes, the hole is there so the SBC can be turned from the outside. Not necessarily recommending it but I am a chronic experimenter and it's working for me.

The adjustment shaft of the SBC is not detented in either position but can't do the 180 rotate when installed due to a little extension which the inner wall of the upper receiver would prevent from moving. So in addition to the hole I had to create a little clearance in the bore of the upper so the shaft can flip over.

[domestique]

Those are good considerations that I didn't think of.
I like to have rifles that are complete, though. No way would I want to have to have to borrow parts from one rifle to make another functional.

Depends on the upper and user situation.

Perfect example:

I have a couple MRP uppers with 2-4 barrels per upper. I'm already swapping bolts back and forth. Cost wise it is a LOT cheaper to have 1 SBC per upper then to send each barrel to Marvin Pitts to hydraulic press each gas block off and install a 45 degree gas block to each barrel.


If I was building a upper from scratch, then I would definitely go Micro MOA gas block or similar.