Interesting goings on going on, and one of them is constant tinkering with the Mk 18 carbine in the SOF world. One of the things people are doing is running them suppressed sometimes, and not suppressed other times. The word is that this bolt carrier helps make that change in a regular, direct impingement AR like the Mk 18.
The Mk 18 (or the CQBR upper for the M4A1, which produces the same functional weapon) is widely issued within SOCOM and somewhat beyond it. For example, Marines who need such a carbine have them, but Uncle Sam’s Military Club runs them with some different accessories than the SOPMOD gear commonly used in the other branches’ SOF.
Running suppressed is more and more widespread (in conventional forces as well as in SOF). But there are several downsides to a suppressed DI AR. Taken together, these add up to one of the key impetuses to the development of the piston HK 416. But experience has shown arms developers that it’s possible to make a DI AR run well, while suppressed; what has been a challenge is to make the same AR run equally well with the QD suppressor on or off.
To recap the problems:
- More pressure than designed into the gas system, yields…
- More blowback out of the ejection port, plus…
- Much higher carrier velocities, producing
- Higher perceived recoil
- Higher cyclic rate on AUTO
- Reduced reliability, and
- Reduced durability.
Gemtech’s solution is so simple that the instructions for using it are pretty much contained in these two box cover illustrations:
The valve flange is on the left side of the bolt carrier. To change it, then, you must remove the BC from the firearm. You can then turn the valve flange to (S) for Suppressed or (U) for, you guessed it, Unsuppressed.
When you’ve made such a change, or, for that matter, at anytime the GemTech Suppressed Bolt Carrier is installed, an indicator visible through the ejection port shows whether you’re configured to run Suppressed (S) or Unsuppressed (U). That’s pretty much it. The setting indicator arrow points aft to S, or forward away from S, and makes the whole system fairly Ranger-proof.
The GemTech bolt carrier is adjusted with a flathead screwdriver, but other tools will work in a pinch. The valve can get a little gummy.
The GSBC comes with the carrier key screwed and staked in place, but otherwise it is a bare carrier. It is conventionally notched for use with a forward assist. It lists for $249 and can be bought direct from Gemtech or from Gemtech dealers.
Gemtech’s claims of reduced carrier velocity and reduced cyclic rate are supported by an analysis by Philip Dater, available on the Gemtech website (.pdf). The reduction was significant on several different weapons, but much larger (25%) on an M4A1 than on a Mk 18 (16%). Still, that’s not trivial.