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AR-15 Buffers and Weights Explained

The AR-15’s Buffer System Is Often Overlooked When People Are Building A Rifle

However it is a necessary part of the function of the rifle. This is because the gas and buffer system work together to cycle the gun.

Let’s look at AR-15’s buffer system before we look at the different weighted buffers.

AR-15 Buffer Overview

The AR-15’s lower receiver features a simple, but necessary projection on it. This projection is called the buffer tube or buffer assembly. Usually we think of it as the place we connect our stock to, but it is more than that. It consists of the buffer tube, the buffer/recoil spring, and the buffer itself.

Buffer Tube and Castle Nut

This is the “outer shell” of the buffer system. It connects to the AR-15’s lower receiver and houses the buffer and buffer spring. They are usually made of aluminum and are semi-universal.

The tube is connected to the lower receiver with a castle nut and a latch plate. If these are improperly installed, the buffer can damage itself and other unnatural wear can occur.

Buffer/Recoil Spring

The buffer or recoil spring has three primary functions. The first function is to slow down the reward travel of the bolt carrier group (BCG). The next function is to return the BCG forward while causing the BCG to pick up the next round. This is the most important function since it readies the gun to fire again.

Finally, the recoil spring can help reduce felt recoil when firing the rifle. This is why it is usually referred to as the recoil spring, but this places the emphasis on a secondary role of the spring instead of its primary role.

Buffer/Buffer Weight

The buffer is a small capsule that is held inside the buffer tube and sits in the recoil spring. Inside it there are small weights made of either steel or tungsten. These weights add the necessary mass to the buffer so it will work with your particular rifle.

If the weights are too heavy and your cartridge is too weak, the gun can experience failures to eject. If they are too light, the gun will beat itself to pieces by recoiling violently with powerful loads. Selecting the right weight depends on the gas system and ammunition used in addition to if the gun is suppressed or not.

Different Types of Buffer Weights

We’re going to go over the most common buffer types while making a few assumptions. Selecting the right one for you depends on how much gas is being put into your gun by the cartridge. This depends on the size of your gas port, so if you know its dimensions you’ll be able to select a buffer easier.

Carbine Buffer

Carbine buffers usually weigh 3 ounces and use 3 steel weights. This is best paired with a mid-length gas system and a 16-inch barrel when using 5.56/.223 ammunition. While it can work with a carbine-length gas system, it will feel overgassed and have more felt recoil.

If you are going to use .300 Blackout, it’s better to use subsonic ammunition and a pistol-length gas system in order to achieve the necessary pressure to cycle the gun.

H buffer

The H or Heavy buffer is 3.8 ounces and uses 2 steel weights and 1 tungsten weight. This buffer can eat up recoil and is usually used when a gun is over gassed. If your rifle unlocks too soon, the H buffer can be the solution, especially if the current buffer is too light.

This buffer works with carbine-length gas systems in 5.56 and subsonic .300 Blackout guns with pistol gas systems.

H2 Buffer

The H2 buffer is heavier than the standard H buffer. It weighs 4.7 ounces using 2 steel and 2 tungsten weights. It is the best option for a carbine-length gas system with a 16 inch barrel and works with a mid-length gas system. It can produce more felt recoil when paired with pistol-length gas systems, but it is the best option compared to the standard H buffer.

You should not use it in a rifle designed to use subsonic .300 Blackout with a pistol-length gas system since it can fail to fully cycle the gun.

H3 Buffer

The H3 buffer is one of heaviest options and weighs 5 ounces using 3 tungsten weights. This buffer is best in very short AR-15 builds, usually 5.56 guns with 9 inch to 11 inch barrels using pistol-length gas systems. This helps keep felt recoil down in such a short system.

When combined with the appropriate spacer (0.76 inches to 0.875 inches total), an H3 buffer can be used instead of a conventional 9mm buffer since they weigh roughly the same. If you don’t have spacers, U.S. quarters can be used as an alternative.

HSS Buffer

The HSS buffer is even more focused on AR9s and usually weighs 6.5 ounces using custom weights. These weights can be made of tungsten combined with a stainless steel housing. These are specifically used to reduce recoil for over-gassed AR9s that still have heavy recoil using AR9 specific buffers or H3 buffers

XH Buffer

The XH buffer is for the most high recoiling platforms and weighs 8.5 ounces using 5 steel weights and a spacer. These are designed for 9mm +P AR9s and .308 or 6.5 Creedmoor rifles. These generally won’t work with standard 5.56 rifles, but they can work in pistol-length gas systems with larger-than-normal gas ports.

Rifle Buffer

This type of buffer is no longer used. It was the buffer style used in the original fixed stock M16, but today all buffers follow the carbine pattern. If you encounter one, it may indicate that the rifle you have is an original piece.

Additional Buffer Considerations

While most buffer sets are compatible across most AR-15 lowers, there are some exceptions. This either comes from larger calibers or specialized needs.


AR9s generally run the best with specially designed buffers. But this is not always the case. Heavier buffers like those mentioned above can be used with AR9 platforms. This is because more mass is needed in an AR9 because it is a direct blowback system. The bolt carrier and buffer provide the necessary mass to seal and cycle the gun.


While the buffer tube is interchangeable between the AR-308/AR-10 and the AR-15, the buffers themselves need special attention. This is to ensure the correct level of bolt travel in the large caliber system.

Most modern AR-308s and AR-10 use a mid length gas system and a carbine tube while using a buffer weight ranging from 3.8 to 5.5 ounces for the best results. DPMS style AR-308s require a carbine length tube while other options just need to be matched with the correct tube/buffer combo. For instance rifle length with rifle buffer, carbine with carbine.


Choosing the correct buffer and tinkering with buffer weights is a great way to optimize your rifle for the best performance. However if you tune your rifle too much it may have trouble using a wide variety of ammunition or working outside of your tuned parameters. This is mostly found in suppressed rifles or other high stress guns.

You need to determine if the buffer selection effort is worth the time and cost for refining your rifle. If it is not, the standard buffer your rifle came with will be enough.