Brownells Gun Techs and debunkers of misguided firearm myths Caleb and Steve usually keep things light. But today they delve into a heavy topic: the common belief that an AR-15 chambered for a "heavy" caliber - .300 Blackout, .350 Legend, .450 Bushmaster, etc. - requires a heavier buffer. Heavy caliber = heavy buffer.... Seems logical, right? Actually, NO. The AR-15 bolt / carrier system is designed to handle a certain amount of gas pressure, and the gas port up front on the barrel is drilled to provide the right amount of gas flow to cycle the gun reliably with a standard 3 oz. buffer. A blowback-operated pistol-caliber upper in 9mm Luger, .40 S&W, or .45 ACP DOES require a heavier buffer to manage the higher pressure of the direct-blowback gas. An AR-308 has a heavier bolt / carrier group, so it needs a heavier buffer to push the BCG back into battery. Sometimes, a heavy buffer is needed to tune your system for short barrel lengths, to slow down the cyclic rate on a full-auto AR-15. A heavy buffer can also be used to slow down the recoil impulse to reduce felt recoil - but the gas flow has to be adjusted to work with that heavier buffer. Most of the time, the standard 3 oz. buffer works just fine. So the myth is BUSTED. You do not need a heavier buffer on an AR-15 chambered in a heavy caliber.