AR-15 Buffers, Springs & Weights Explained

It's a small, unremarkable little part, but it's one of the most important pieces in your AR-15: We're talking about the buffer! The buffer and recoil spring in your black rifle (or pistol) helps manage recoil but more importantly, it controls the action of the bolt carrier group (we wrote a guide on the AR-15 BCG, too) and it helps your weapon cycle any ammo you run through the magazine. If you're here, you're probably hunting for the answer to the a question: What buffer weight is best?

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The AR-15 Buffer

The buffer has three jobs:

1. Absorb the energy of the bolt carrier group as it compresses the spring inside the tube.
2. Push the bolt carrier group back into the upper receiver, chambering another round.
3. Reduce and control felt recoil for the shooter.

The buffer's flat face rests in front of the spring at the opening of the tube, captured by a small detent. The body of the buffer and the back with the "pointy thing" (short absorber) rests inside the spring. The pair rest inside the buffer tube, and the tube is secured to the upper receiver using a latch plate and castle nut.

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How it Works

The spring compresses as the BCG slams against the buffer, driving it backwards into the tube. The spring reaches its limit and then rebounds, pushing the buffer back to the front of the tube, forcing the BCG back into the upper receiver. This entire process happens in less than one second:

Buffer Weights Compared

Grab a buffer and jiggle it next to your ear, and you'll hear some rattling inside. That's coming from the weights inside the buffer. The weights, separated by small rubber pads, are the real buffers. They work to absorb most of the recoil imparted on the buffer by the BCG. Without these weights (and a little wiggle room to let 'em dissipate all that energy), the buffer would just transfer all that energy straight into the buttstock - and your shoulder. Lighter buffers move quicker, absorb less energy, and require lighter ammunition loads. Heavy buffers move slower, reduce recoil more, and require heavier-grain loads.

The Golden Rule

You should run the heaviest buffer that still allows your rifle to cycle completely and reliably, with the ammo of your choice. Have too little weight, and recoil will feel punchy. You'll also wear out your receivers, buffer, and BCG quicker. Have too much weight, and you'll suffer from jams, or your AR won't cycle at all. So, which weight do you need? 

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Available Weights

Carbine (3.0 ounces)

• (3) Steel weights

The carbine buffer is usually the gold standard for commercial rifles. Most store-bought AR-15s use a carbine gas system and 16" barrel, which often requires a carbine buffer. This setup is designed to reliably cycle nearly any type or 5.56 or .223 ammunition. Recoil is moderate and reliability is very high. Carbine buffers are also commonly used in mid-length gas systems. Reliability is still high, but felt recoil is reduced.

Heavy H (3.8 ounces)

• (1) Tungsten weight
• (2) Steel weights

Many find that store-bought AR-15s are "over-gassed", meaning the carbine gas system punches too hard and rocks the BCG violently. If recoil is excessive, many shooters choose to swap out the carbine buffer for a beefed-up "H" buffer (20% heavier) to alleviate felt recoil and reduce wear on the gun.

H2 Buffer (4.6-4.7 ounces)

• (2) Tungsten weights
• (1) Steel weight

H2 buffers are what shooters choose when even an "H" buffer feels too punchy, or if they want to reduce recoil as much as possible without suffering cycling issues. H2 buffers usually perform well in carbine gas systems, though not always. Every AR is different. H2 buffers are also quite popular with pistol gas systems. They're usually found in 300 Blackout-chambered guns or shorter AR pistols chambered in 5.56/.223.

H3 Buffer (5-5.4 ounces)

• (3) Tungsten weights

Just like how carbine-gassed rifle owners might swap out a carbine buffer for an H buffer because it feels too punchy, 5.56- and .223-chambered pistol shooters may do the same thing by swapping out an H2 for an H3. Simple.

Pistol Buffer (5-8.5 ounces)

• Custom weights/housings

Some AR-15 pistols and carbines are chambered in an actual pistol round, like 9mm. These pistol cartridges use blow-back operation to cycle the bolt, instead of a delayed locking bolt and conventional gas tube with key. The added pressure and energy produced by blowback operation might mean you have to ditch the standard buffer entirely. You might need to buy a custom pistol-caliber buffer for your AR.

Pistol-caliber buffers usually ditch the aluminum housing for a steel housing, which accounts for some of the required extra wight. Some pistol buffers will use standard weights, or they might use custom weight or different innards entirely.

Rifle-Length Buffer (5.0 ounces)

• (5) Steel weights
• (1) Steel spacer

WARNING: Rifle buffers are only to be used in an A2-style fixed buttstock.

The rifle buffer is the quirky, have-to-be-different, original AR-15 buffer. The rifle buffer was developed when the AR-15 was first designed with a fixed stock and longer buffer tube (measuring 9.625"), which was later adopted for the service-issued M16 rifle (until it was upgraded with a collapsible stock). These longer buffers won't fit in the standard carbine tube (measuring 7.625") commonly found on the modern AR-15, and trying to use one without the right tube or stock could be dangerous. It certainly won't work.

How to Add or Remove Buffer Weight

You don't need to buy a new buffer just because you want to add or remove weight for the sake of recoil and functionality. Buffers can be expensive, too. Instead, you can easily take apart your buffer and simply buy heavier tungsten or lighter steel weights. All standard buffers use a small Allen-head set screw that traps the plastic bumper, keeping the weights and rubber pads inside. Simply remove the set screw to swap out the weights.

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Silent-Captured Buffer & Spring Kits

Conventional buffer tubes like to clang around - especially with all those dead weights and the "give" between them - and they can feel springy. If dirt, dust, or grime gets in the tube, all that mess will make the buffer and spring feel gritty, too. Silent-captured spring-and-buffer kits combine the two components into one, eliminating most of these drawbacks.

Silent-captured buffers "lock in" all the weights to a single post with rubber grommets, and there is no hollow housing to shimmy around and make noise and vibration. The recoil spring is also wrapped around an operating rod, preventing it from bowing and moving around when it compresses. The base of the spring also features a rubber pad to absorb the recoil against the buttstock, which further eliminates noise. Silent-captured run much more smoothly and quietly with no drawbacks.