Of all the parts on an AR-15, the buffer is perhaps the most insipid. It spends its life hidden in the receiver extension, and when pulled free, it does little to cause excitement. Flat on one end, round in the middle, with a "thingy" on the other end, it's rather boring to look at. Shake it next to your ear and you'll hear something rattling about inside. But what does it do, and how can it be hot-rodded to your benefit?
To operate reliably with a diverse array of loads in conditions ranging from extreme heat to extreme cold, even when dirty, requires a careful balancing act. An AR needs to have enough gas tapped off to cycle the action forcefully but not excessively.
If too much gas is tapped off, felt recoil and wear on the mechanism is increased. Too little and the action will not cycle properly, leading to malfunctions, failure to feed or failure of the bolt to lock back on the last round.
Typically, a factory AR carbine will normally be a bit over-gassed to ensure reliable function even in extreme conditions. While being a bit over-gassed aids reliability, it is not always advantageous or even desirable. This is especially true for recreational use or for various types of competition where a lighter-recoiling and smoother-operating cycle is desired. For such use it is possible to tune how the carbine cycles by adjusting the weight of the reciprocating mass: the buffer.
Simply increasing the buffer weight of the reciprocating mass can provide noticeable benefits, including reducing felt recoil and muzzle movement and providing additional mass to aid feeding during the loading cycle. The easiest and most cost-effective way to do this is to simply replace your standard buffer with a heavier model.
If you take apart a standard carbine buffer (which requires only a punch and a hammer: simply drive out the retaining pin and pop off the synthetic pad), you'll find three steel weights and three rubber pads inside. If you weigh a standard buffer, you'll find it's three ounces; the steel weights and the pads account for about 1.9 ounces of that.
Carbine buffers are available in a variety of weights. Colt developed heavier models for certain applications, including the H1 (3.8 ounces), H2 (4.6 ounces) and H3 (5.4 ounces). The H1 uses two steel weights and one tungsten weight, the H2 uses two tungsten and one steel weight while the H3 uses three tungsten weights. If you have a standard buffer and you buy an H3 buffer you can use their weights to build both an H1 and an H2.
Colt's H series is the most common, but there are also other buffer weights and designs available from the aftermarket. My favorite, which I have used for years, is MGI's Rate and Recoil Reducing buffer. The MGI buffer features tungsten weights combined with a spring-loaded shock absorber. Its 7.1-ounce weight (more than twice as heavy as a standard buffer) provides a slight delay in bolt unlock timing. This provides extra time for the swelled case to release its grip on the chamber wall, aiding extraction.
The bolt/carrier/buffer's rearward movement is also slower due to the increased weight. When the MGI buffer strikes the rear of the receiver extension, its mechanical plunger propels the internal tungsten weights forward. These contact the rearward-moving buffer body (internally) and cause a cancellation of the rearward movement just prior to bottoming out. The masses then come to a complete stop, eliminating much of the felt recoil that would otherwise be transmitted to the shooter.
When the recoil spring drives the buffer/carrier/bolt assembly forward, it is also at a slower speed. This provides additional time for the magazine to present the next cartridge. However, it has greater momentum due to the increased weight, which aids feeding. After the bolt locks, the MGI's internal tungsten weights provide a follow-up hit into the front end of the buffer, eliminating bolt bounce. Felt recoil is noticeably reduced. The only downside is its cost: $165.
Another option is HeavyBuffers.com, which offers a wide variety of AR buffers, 9mm buffers, AR-10 buffers and special designs for Vltor's A5 system and LWRCI's UCIW short receiver extension. The HSS features a stainless steel body, tungsten weights and beefy 6.5-ounce weight. The XH model is the heaviest on the market, tipping the scales at 8.5 ounces—almost three times the weight of a standard unit.
Both the HSS and XH are machined from solid 303 stainless steel and sport a smooth, polished finish. They are assembled using tungsten anti-bounce weights, stainless steel roll pins and synthetic pads. They're nicely made and quite effective. Price is $75 for the HSS and $125 for the XH.
Adding weight to the reciprocating mass is just one possible solution. Another route preferred by competition shooters is to go with a lighter buffer weight, which reduces felt recoil and allows quicker recovery between shots. However, if you do this, you must replace your standard non-adjustable gas block with an adjustable unit because you have to turn down the gas flow with the lighter buffer weight.
One option is Taccom's LW AR-15 recoil system, which features a Delrin buffer weighing less than one ounce. Price is $23 for a carbine-length buffer and $25 for a rifle-length buffer.
My final thoughts. If it's a service gun, leave it alone. If it's over-gassed, and you don't have an adjustable gas block, adding a heavier buffer can noticeably reduce felt recoil.
If you do have an adjustable gas system, reducing buffer weight can do wonderful things. Don't be afraid to experiment and have fun with Stoner's wonderful creation.