AR-15 Gas Block – What to Look for When Buying

The gas system of your AR-15 is an absolutely essential part of your rifle, and the AR-15 gas block is an essential part of the gas system. The basics of the first half of the AR-15 firing cycle are as follows:  When a weapon is fired, the gas from the round travels through a port in barrel, up through the gas block, and into the gas tube.

Traveling through the gas tube, it reaches the gas key that is attached to the bolt carrier group, pushing the bolt carrier group rearwards into the buffer and buffer spring inside the buffer tube.

Once the buffer spring reaches full compression, it starts to rebound and the second half of the firing cycle begins.

Just like almost every other part made for the AR-15, there are many different types of AR-15 gas blocks available. The right gas block may not only improve the aesthetics of your build, but it can also improve the function of your rifle. In fact, this small AR-15 part can actually reduce recoil and wear, increase reliability, give you the option to run suppressed or unsuppressed, and more. There are several important factors to keep in mind when shopping for the gas block you want to run on your custom AR15 build.

AR-15 Gas Block Adjustability

Gas blocks come in both standard and adjustable formats. Most standard gas blocks allow a set amount of gas to flow through the system. Some allow more gas in than necessary, called “overgassing”. This is especially helpful when there is carbon buildup or when there is other debris that partially blocks the gas flow in your AR. With overgassing, your gun can continue operating even with a partial blockage, which is nice with regards to reliability.

However, when higher temperatures combine with the excess gas from “overgassing”, it can also create quite a bit of additional carbon residue that leads to a buildup. So essentially, overgassing your AR “fixes” a problem that it also helps cause.

Nevertheless, standard gas blocks have the advantage of being much more simple (no adjustments are needed) and easier on your wallet.

Adjustable AR-15 Gas Blocks

Adjustable gas blocks allow you to change the amount of gas flowing through the block itself. They are considered an upgrade to standard blocks and can actually take your gun to a whole new level of performance, depending on your needs. Proper use results in a cleaner system overall, less felt recoil, and less wear on your firearm.

On a basic level, there are a few adjustable gas block options, the “cut-off” type and the “bleed off” type.

One of our favorite picks for a “bleed off” type adjustable gas block is the Superlative Arms Adjustable Bleed Off Solid Block.

Instead of restricting the flow of gas like conventional adjustable blocks, it has a 30 position adjustable system that regulates the gas flow by “bleeding” it out of the front of the block, pushing it away from the shooter.

As mentioned previously, there are also ‘cut-off’ type adjustable gas blocks that literally have an “OFF” setting on the gas block. These types of gas blocks are generally used for people who are primarily running suppressed and want a way to shut off the gas system completely.

The Noveske Switchblock Gas Block is a prime example of a ‘cut-off’ type gas block with its 3 settings, unsuppressed, suppressed, and OFF.

If you are going to run an AR-15 that will be suppressed for the majority of the time, you may want to look into a ‘cut-off’ or ‘closure’ type gas block for your build.

Low Profile AR-15 Gas Blocks

Both adjustable and standard gas blocks come in low profile versions. “Low profile” simply means that the blocks are machined with precision to take up the least amount of space possible on the barrel of the gun. Before making a purchase, you might want to measure the space allowance on your barrel so you can choose the perfect size for your build.

AR-15 Gas Block Size

AR-15 Gas blocks come in different sizes to fit onto the gas journal of various diameter barrels. For example, gas blocks with an inner diameter measuring 0.625” inches will typically be used for “Pencil” type barrels or thinner lightweight barrels.

“Standard” barrels, are generally considered to be medium-sized and are normally paired with gas blocks that have a 0.750” inch inner diameter. You’ll probably notice that 0.750” is a commonly available size.

Finally, some gas blocks are made to fit what are known as “Bull Barrels” or what are generally considered to be the thickest barrels for the given platform. A “Bull Barrel” is usually larger and heavier than a standard one. In most cases, 0.875” and 0.936” inner diameter gas blocks are the standard size used for these barrels.

Just be sure to measure the diameter of the gas journal area on your barrel before choosing which gas block is perfect for your AR-15 build.

AR-15 Gas Block Price

In general, adjustable gas blocks will cost more than standard ones, due the designing, engineering, and CNC machine work needed to make them. The specific materials used are another factor that affects their price. Most gas blocks are made from steel and are nitride treated for durability.

Any way you decide to go, the gas block you choose will make a difference in how your AR performs. So choose wisely, buy what fits within your budget, and make sure whatever you get is going to accomplish your specific goals.