300 Blackout is a massively versatile round that, as we’ve said many times already, can be shot reliably and accurately with suppressed and unsuppressed loads – all without having to change your rifle, SBR, or pistol configuration. But to pull this ballistic magic off, you need to have your AR 15 set up to manage these wildly different loads without issue. Let’s break down the proper configuration you should be sticking with, so when you twist a can onto those 5/8 x 24 threads, you get nothing but satisfying little whiffs and the sound of pinging steel.
Of all the different “things” that go into suppressing an accurate AR 15 chambered in 300 Blackout, the topic of barrel length is perhaps the most hotly debated. Community experts have run the numbers, tested out different barrel lengths, measured shot groups, and duked it out on forums.
The results are in: You should be sticking with a barrel that ensures optimal velocity (just under 1,125 fps, the magic subsonic number) while retaining a generally ergonomic, not-feet-long gun. For most folks, that means sticking with a 9” barrel. Yes, 9” is the magic number. Beyond this length, you’re getting diminishing returns on stabilizing your load and achieving optimal velocity. Anything shorter than 7.5” is generally considered to provide sub-par accuracy – and yes, .300 Blackout, even suppressed, is very accurate, usually offering 1 MOA accuracy at 100 yards. Pretty impressive.
And as far as twist rate is concerned? That depends on your gun’s application. Will you be shooting only suppressed, or will you dance around with supersonic loads? If you’re only shooting suppressed, stick with a 1:7 twist rate. This is optimal for handling those super-heavy subsonic loads. If you want to shoot both, stick with a 1:8 twist. This will still stabilize subsonic loads, but it’ll help with keeping those lighter, supersonic loads in check.
This one’s simple: Stick with a pistol-length gas system. Although carbine and pistol uppers look alike at first glance, their gas systems are wildly different. The former measures 7”, while the latter measures just 4”.
The logic here is easy: A pistol-length gas system will easily handle any .300 Blackout load, but a carbine-length gas system will not reliably cycle subsonic, suppressed loads every time. There’s simply too much distance for the gas to travel before it reaches the bolt carrier group, resulting in possible failures to cycle. Why is it so finicky, you ask? Subsonic loads just use a very small amount of gunpowder.
The buffer and spring that controls your bolt carrier group matters just as much as your gas system when it comes to shooting subsonic, suppressed .300 Blackout. The heavier the buffer, the more back pressure is needed to compress the buffer and spring – resulting in more likelihood that your bolt carrier group will again, not cycle properly.
We recommend sticking with your common H1 and H2 buffers. Unfortunately, there are so many variables that play into the proper buffer that you may have to experience. What we can tell you is this: If your 300 Blackout gun isn’t cycling and reloading after each shot, your buffer’s too heavy. If your bolt isn’t locking back to the rear when your mag runs dry, or if your recoil feels a little too snappy, your buffer’s too light. Popular opinion rests with the H2 buffer, weighing in at around 4.7 ounces. The H2 is said to reliably handle both supersonic and subsonic loads reliably.
Suppressing a Rifle in 300 Blackout
That’s all folks – above are all the factors you need to consider when building a proper sub gun in 300 Blackout. The above recommendations will afford you an SBR or AR Pistol that’s compact, reliable, and accurate with any 300 Blackout load.
We’ll end with this: Yes, suppressing a 300 Blackout rifle is just as fun – you’ll just end up with a long barrel assembly. Every suggestion above remains valid if you decide to suppress a 300 Blackout rifle.