The community of users among gas-gun enthusiasts is a bit divided over the merits of an adjustable gas block. It is not a process that is terribly intuitive or easy to tackle for the first time. Many shooters have plenty of questions: How do I adjust it? How much gas is enough, or too much?

This advice will hold true for most gas-driven firearms. Whether the piston is external— like on the BRN-180— or direct impingement, such as in the AR-15, the basic operating principle is the same. Pressure from the burning powder is diverted from the barrel and is used to cycle the action. Early semiautomatic weapons relied on the recoil of the round to drive the bolt back. The introduction of a gas system was a significant step forward in weapons technology. One of the ways engineers prioritize reliability is to over-gas the gun, to deliver an excess of energy than the action needs to cycle. Adjustable gas blocks allow the user to control the energy introduced into the action.

Most piston systems are either ‘long stroke’ or ‘short stroke’. A short-stroke piston has an actuator rod that floats independent of the piston head and the bolt. When the piston moves, it forces the actuator rod back. This in turn impacts the bolt and transfers the force from the gas port. In long-stroke pistons, the actuator arm and piston head are connected to the bolt in a single unit, rather than operating independently.

Short-stroke pistons tend to have a shorter operation cycle and require more up-front energy to guarantee consistent cycling. Long-stroke pistons have a longer cycle and therefore less felt recoil, but the inertia of the heavier mechanism requires a more sustained gas pressure peak to operate it properly.

The direct impingement of the AR-15 was a novel evolution. The bolt carrier group is (technically) a linear piston directly behind the chamber. This includes the gas key and the gas rings behind the bolt itself. This design puts the reciprocating mass of the piston behind the barrel rather than underneath or attached to it, with excess gas being vented into the space behind the bolt.

How to Adjust The Gas Regulator

When adjusting the piston system, start with an empty magazine. Load one round into the magazine, feed it into the chamber, and fire. Observe where the brass goes. Open the gas port up more, load a single round more, and fire again. Do this until the brass is consistently ejecting from the chamber. If the brass is landing more than 3-6 feet away, or notably ahead of your position, you are likely over-gassed and should dial back.

If your gun has a last-round bolt-hold-open feature, keep opening the gas port up until the bolt is consistently locking back on the empty magazine. Every gas piston system is different; some have only a few coarse settings and some are adjustable from 0% to 100%. I recommend going to a setting just beyond the bare minimum of functionality. This will help offset energy lost due to fouling as the gun is shot.

Adding a suppressor tends to increase the gas pressure in the system. Some cans, such as the Huxwerx designs, advertise ‘flow through’ technology that reduces backpressure. You will need to confirm with your manufacturer. The choice of bullet matters here also. Heavier rounds have more ‘dwell’ time between passing the gas port and leaving the barrel, so you get a longer pressure spike. However, subsonic ammunition may have much less powder behind it and will have less energy overall. In my subsonic guns I tune them to run reliably with un-suppressed subsonic rounds. This ensures reliability, but significantly increases wear and tear on the gun due to the increased gas pressure from supersonics.

For duty-grade guns we recommend a coarse gas block adjuster that is easily accessible with no special tools. These guns get shot a lot and see a lot of adverse use. ‘Normal’, ‘Suppressed’, and ‘Open’ offer less fine-tuning but are easier to use and adjust on the fly. Many commercial gas blocks use simple screws as gas regulators; the problem therein is that the screw can walk out under recoil. It is also difficult to quickly change your gas settings in the middle of a crisis situation. They are an economical option for more casual shooters but not ideal for professional end-users.

We are generally fans of adjustable gas blocks. They can not only make guns run more reliably, they can also reduce felt recoil by considerable amounts. That said, they are a tool that requires some intelligence to calibrate correctly. You should practice with your guns enough to know when the gas system is in need of cleaning or needs to be adjusted to add more gas to a dirty or dry system.

Adjusting Adjustable Gas Blocks