Silencer Shop Authority: Gemtech Suppressed Bolt Carrier Review
When shooters first suppress AR-15s, the first thing they typically notice is the increased backpressure that throws smelly gas and debris into a back into the user’s face and significantly dampens the fun. For those behind a fully automatic rifle, the problem is even worse as the backpressure contributes to substantially increase cyclic speeds. This leads to unpleasantly high rates of fire and increased parts wear. Traditionally, the preferred mitigation approach for suppressed blowback has been to install an adjustable gas block capable of regulating gas pressure before it ever reaches the receiver, but this may not work in some situations. For those who are not able to swap their gas block or who own multiple uppers that share a single bolt carrier group, Gemtech has developed an alternative solution, the Suppressed Bolt Carrier (SBC). Curious to see how the SBC stacks up, I talked to the guys at Silencer Shop and had them send one my way for further review.
Design
Conceptually, the SBC is an awesome piece of kit. It outwardly resembles a garden variety AR-15 bolt carrier, and installation is the same as the standard part. Beyond the prominent Gemtech logo on the right side, the only real visual departures from a factory AR-15 part are the small switch on the left side of the carrier and the “S” (suppressed setting) indicator on the right of the unit. For ease of use, the gas switch can be flipped between settings using a flat head screwdriver for case rim.
Like some adjustable gas blocks, the two settings allow shooters to open (suppressed) or close (unsuppressed) a small gas port on the right side of the carrier. In the open suppressed setting, excess gas is allowed to flow from the gas key through the SBC and escape out the ejection port through the aforementioned hole. Flipping the valve to the suppressed setting also restricts gas flow into the carrier’s expansion chamber. This design reduces (or more appropriately, slows) the amount of force applied by the gas to the bolt carrier group and slows the rifle’s cyclic rate. It really is an interesting take on a rather simple set of principles.
The carrier itself is made of 8620 steel and weighs exactly as much as a standard M16 carrier at 9.5 ounces. While the SBC does not appear to be chrome lined, the finish seems to be a nice nitride treatment, which makes for easy cleaning. To round the package out, the gas key screws are prominently staked, so they should not be going anywhere.
Range Report
Testing the SBC turned out to be a more interesting endeavor than I initially expected. My expectation was that the carrier would make a huge difference in felt recoil while using a suppressor, but this was not the case. On my semi-automatic SR-15, the practical difference between a standard bolt carrier and Gemtech’s (on the suppressed setting) proved to be relatively minor. However, the Knights upper is universally considered one of the softest shooting on the market. In fact, many SR-15s struggles to cycle low powered ammunition as there simply is not enough back pressure to cycle the bolt and carrier. Since backpressure is the force that drives carrier speed, a gun that already manages gas reasonably well may not benefit from the SBC like other, gassier rifles do.
Though I’ve downplayed the effect that the SBC had on my SR-15, I would be wrong to say that it had no impact. With my Specwar 556 and the SBC on the unsuppressed setting, the bolt carrier was bottoming out and bouncing at the rear of the receiver extension, resulting in a rather jarring recoil impulse. By comparison, when flipped to the suppressed setting, the SBC seemed to cycle less violently. It should be noted that while the difference between the two settings was noticeable, the experience was much like tasting similar wines in that I had to pay close attention to tell them apart. To further elaborate, Gemtech’s testing showed a mere 5.5-millisecond difference in chamber opening times (5,741 mm/s vs. 4,061 mm/s) between the SBC on its suppressed setting and a standard bolt carrier on a 14.5 inch M4. By a percentage, these results are impressive, but it is the sort of difference that can be difficult to detect when you’ve just dropped the hammer on a 5.56mm or 300 BLK round. Interestingly, the same tests showed a much larger improvement on the shorter, 10.5 inch MK18, where the bolt carrier group’s opening velocity dropped from 7,239 mm/s to 5,346 mm/s. Based on these numbers, shooters with short-barreled rifles are likely to find the SBC particularly enticing.
I did not notice it in my initial assessment, but the slower carrier speed may be clear in the video posted below. Viewers will not be able to see the actual difference as the firearm cycles. Still, in the second string, the brass appears to exhibit slightly slower (in that it can be seen) and more consistent at 3 o’clock ejection. This lends credence to Gemtech’s claim that the cyclic rate with the SBC on the suppressed setting is indeed reduced. Please forgive my stupidity at the beginning of the second string; I forgot that I had removed the bolt carrier group and, thus, cleared the chamber.
As far as gassiness is concerned, I really could not tell the difference between the SBC and a standard bolt carrier. Gemtech advertises reduced blowback with their carrier, but based on my experience, I would not purchase the accessory with the singular goal of controlling gassy blowback. When possible, adjustable gas blocks are still the optimal solution for gas management.
One thing I would like to see changed on the SBC is the placement of the suppressed/unsuppressed switch. Situated on the left side of the carrier, the gas valve is impossible to toggle without removing the entire carrier group from the rifle. To assist in switching between gas settings, I think it would make more sense to allow for adjustment through the ejection port on the right side of the rifle.
Conclusion
Gemtech’s SBC is a difficult product to judge. On one hand, the carrier does everything that Gemtech says it does. It reduces the rifle’s cyclic rate (slowing parts wear and reducing recoil) and does partially cut down on blowback. However, the other side of the argument is whether or not such functionality is worthwhile for most shooters. The majority of people probably will not notice differences in cyclic speed on semi-automatic firearms and I feel that shooters really need the “fun switch” to appreciate all that the SBC has to offer.
On the whole, I can recommend the SBC for owners of fully automatic AR-15s/M16s, especially those who cannot or do not want to use an adjustable gas block. The system is essentially plug and play and works well to manage cyclic rates. SBR owners are also likely to enjoy the SBC. Most short AR-15s become seriously over gassed when suppressed, and the numbers from Gemtech show that the SBC brings them back to reasonable levels. For your average semi-auto shooter with a Title I (non-NFA) AR-15, the advantages are less pronounced. At $225 from Silencer Shop, the SBC is quite a bit more expensive than a standard carrier, and it may not be a great choice for budget-minded enthusiasts who simply want to mitigate blowback. For these folks, I still feel that adjustable gas blocks are the way to go.
Jeremy Mallette is co-founder of International Sportsman. An avid hunter and outdoorsman, he has spent more than a decade in the outdoor industry, from hiking and camping to silencers and hunting. His father taught him to shoot at age six, and he received his first firearm at age eight — a 1942 Colt Commando .38 special revolver. He enjoys yearly trips to Kansas for pheasant hunting, spending time with his children at the deer lease, and collecting unique firearms.
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