AR-15 5.56

We always start with a suppressor discussion, because with the advent of low backpressure cans, your tuning journey could end with just the right choice of suppressor. As the industry stands today, we don't see many reasons to go with a hybrid or high backpressure design on the AR-15 beyond cost savings. This platform, more than others, is heavily rewarded by keeping gas moving forward, and all of our recommendations will feature some technology to reduce backpressure.

Because the AR-15 comes in so many varieties (long or short barrels, heavy or thin profiles, short or long gas tubes), the number of independent variables can compound quickly. Get a good understanding of what your unique rifle is built with and explore some of the articles we cover on barrel harmonics, weight distribution, dwell time, cyclic rate, etc. It will all be relevant to this platform.

Have a high backpressure can, or want some of the weight or flash characteristics of a traditional welded stack design? That's fine, there are ways to tune for this. And even if you have a hybrid design, the optimal suppressed AR-15 host will still benefit from modifications beyond a reduced backpressure suppressor alone.

The AR-15 platform rarely deviates from the North American standard 1/2x28 thread pattern for 5.56 rifles. If the barrel is wider or chambered in something like .300 Blackout or a larger-diameter caliber, you'll also commonly see the 5/8x24 thread pattern. Check your manufacturer specs for your specific rifle.

The good news: every suppressor manufacturer will have a mount and muzzle device that interfaces with your rifle. The real challenge is taking the time to determine which of the many options you want and ensuring you research which devices are compatible with the suppressor you choose. There are a few mounting options that have compatibility beyond a simple thread pitch match. Things like the Ops Inc collar require a specific barrel contour to interface with. These options are rare and should be very easy to identify. Most mounts you see will be plug and play.

Remember: Do not use a crush washer to time a muzzle device you plan to mount a suppressor to. You risk canting your suppressor and causing a baffle strike or negatively affecting accuracy.

We could get lost in the weeds talking about barrels and suppression. The barrel introduces gas port size and position, which moderates gas flowback into the system. It also introduces barrel harmonics, which affect accuracy, deflection, barrel whip, and any number of nerdy material properties. For the sake of brevity, we'll keep it simple here with a few key considerations.

If your rifle has a large dwell time — that is, the length of barrel after the gas port but before the muzzle — it will be at high risk of running over-gassed with a suppressor. A common example is a 16" barrel with a carbine-length gas system. If picking a barrel for suppressor use, go with a longer gas system, or expect to tune your rifle.

Look also at your barrel's contour. Most popular profiles will be fine with a suppressor. Government, SOCOM, bull, and tapered profiles are all fair game. Some very lightweight, thin-profiled barrels risk deflecting significantly under the weight of a heavy suppressor. This can affect barrel harmonics enough to produce inconsistent groupings, large point-of-impact shifts between suppressed and unsuppressed, and accelerated barrel droop at high rates of fire. If you're running a thin barrel, keep your round count in check and opt for a lightweight suppressor.

Suppressor-optimized barrels do exist. These have no special sauce that makes them uniquely qualified to host a suppressor except having a reduced gas port size to restrict gas flow under the high backpressure conditions suppressors create. They can be a great option for anyone building a suppressed-only rifle who wants to retain the simplicity of the AR-15 platform without novelty parts like a tunable gas block. Just be aware that many of these barrels fail to cycle reliably unsuppressed, effectively making the suppressor a permanent fixture.

This is the most direct method of tuning for suppression. If a suppressor keeps barrel pressure high for too long, delaying the bolt opening by choking off gas at the gas port is the fix. An adjustable gas block lets you open up the gas system if you're underpowered and not cycling, or close it off if things are moving too fast and gas is stacking.

It can also be an effective tool for reducing the sound of a gunshot at the shooter's ear by reducing port pop, the gasses jetting out near your face. Almost all suppressors, even those advertised as low or reduced backpressure, will still produce some backpressure, some port pop, and some ability for both to be curbed with a gas block. And even with a perfectly tuned firearm, switching between higher or lower pressure ammunition can modify the cycling and feel. An adjustable gas block lets you tune that away too.

Why not run an adjustable gas block on every AR? Common concerns center on duty use. Leaving your gas block in the wrong setting in a life-or-death scenario is a risk not worth taking over the downsides of a slightly over-gassed system. There's also the rare but real risk of an adjustable gas block failing. Even if uncommon, it introduces another variable into reliability. For these reasons, my home defense gun runs a fixed gas block and relies on the tuning methods covered in the next chapter.

See our article on adjustable gas blocks for specific recommendations based on use case and price range.

Where an adjustable gas block offers a range of infinite tuning settings, it introduces another variable into the AR-15 reliability matrix. This chapter introduces the idea of a single setting gas restriction device. These come in many forms but all serve the same function: reducing gas flow into the operating system with no moving parts and only one suppressed setting. If the setting is correct, you have avoided the risks introduced by an adjustable gas block being in the wrong setting or failing outright.

The first method has already been introduced: the suppressor-cut rifle barrel. There, gas flow is choked at the gas port itself. A simple, clean method of gas regulation with no risk of failure. The gas port will open up over time, but only after many thousands of rounds as the barrel approaches the end of its service life. This is a great option for those building a custom barrel who can work with a gunsmith to dial in the right port size. Companies like KAK Industries and Sionics offer factory options with reduced gas ports as well.

The next option is the YHM Suppressor Gas Block. This block has a restricted orifice that chokes off gas flow right where a traditional adjustable gas block would, except it is one solid chunk of steel at roughly the same price as a standard gas block. Easy. The only trouble is this single-setting block ships from the factory with one port size. If your barrel does not have a .750 bore diameter, you are out of luck. And if you want a plug-and-play solution, it will only be perfect if the .063 port diameter happens to be perfect for your setup. That said, for a few dollars in drill bits and some basic machining, the port can be opened up to any diameter larger than .063.

Our final option is probably the most popular of the three covered here. The restricted gas tube simple chokes the gas flow as it leaves the gas block. Black River Tactical has a fleet of gas tubes in every port variety imaginable. It is a bit pricier that the YHM gas block, but you can work with a BRT staff to get the exact port size you need. It also has the advantage of being a semi permanent fixture. With simple gunsmithing it can be swapped or removed without needing to deconstruct the whole rifle.