If someone wants to build up an upper that could run both super-and subsonic, there’s going to be some parts mods involved before the cartridge switch.īut! First, it has to run the subsonic. My magazines currently hold my most-trusted Nosler 220gr factory ammo. They’re not normally as overt, but they’re there-extra-quick bolt unlocking, excessive carrier velocity and on down that list. What’s more, subsonic ammo is a good deal lower pressure than supersonic ammo, which has a SAAMI max limit of 55,000 PSI (most is around 50-52,000) most subsonic loads are running 30-35,000.Īnd, yes, a supersonic blackout can have all the same extra-pressure-induced operation symptoms as a 5.56. That’s “port pressure.” Not technically the same as “chamber pressure,” but it’s from the same source. The farther down the barrel the gas port is located, the lower the pressure will be by the time the bullet passes the port and the gas enters the port. No room for a dissertation on gas system operation, but as the gas expands behind the bullet traveling down the barrel bore, an increasingly greater volume is available for the gas to occupy.Īnd, time is also ticking away with respect to the flaming consumption of the propellant.
The pistol-length-port location requires the least amount of post-build tuning to get 100-percent reliability. This is about the only time intentionally ramping up gas port pressure is ever welcome on an AR-15! I’ve written thousands of words about its evils and ways to lower it for other applications. 30-caliber bullet gets put to work effectively because the pressure at the gas port is higher. Run a pistol-length location gas port (four inches ahead of the chamber area) with a carbine-length (16-inch) barrel.ĭone like that, the relatively tiny amount of fast-burning propellant behind that honking. I have found that the best overall approach to subsonic function is to shorten gas system length. One for supersonic, the other for subsonic. Two Blackout barrels: carbine port location on the stainless pistol port location on the other. There’s not enough gas in subsonic, or there’s too much gas in supersonic, for both to function through a system set up more ideally for one or the other. So, despite what I’ve heard from many theorizing, you really can’t run supersonic and subsonic loads through the same gun, with no modifications having been made to the gun. Supersonic would totally overstress this system.įirst, I’m always willing to risk boring knowledgeable readers with really basic information because it’s important to start at the start. This is a 4-inch port location on a 16-inch barrel. A 12-gauge slug “over-penetrates.” Subsonic Architecture A pistol-length gas system has been, for me, a key to getting fresh-off-the-workbench reliable function from subsonic Blackout. That really all has to do with bullet design/bullet engineering.Īny bullet that’s built to either fragment or readily expand (not the same things but about the same effect) isn’t going to get much farther after it meets a solid object. If anything, it’s the heavier bullets that are more likely to keep going. There’s much said, unsubstantiated, about “over-penetration” of higher-velocity bullets. I agree, but not for some reasons commonly given. Just a bit about the whole “defensive ‘rifle’ debate:” some say something like 5.56 is not a good choice for home defense. (Clearly, supersonic Blackout beats it soundly.) 45 ACP is a reliable choice for a defensive round, subsonic Blackout beats it. 45 ACP handgun loading, if we’re going on (the admittedly incomplete) calculated energy figures. 300 Blackout subsonic loads are a little more powerful than a routine. Most subsonic blackout ammo uses a bullet in the 200-grain range, and, of course. That’s another debate for others to work through in other articles, but it’s my story and I’m sticking to it. Plus, I’m a believer in “bigger is better” respecting impact effectiveness of a bullet. 300 Blackout is plenty powerful, in my estimation, and with radically better “shootability” than a higher-pressure carbine loading. Subsonic Blackout has a radically milder blast and report than 5.56 or supersonic Blackout. Now, there are some very effective flash suppressors out there, but they don’t take a bit off the noise.
In the dark, maybe just up out of bed, and then there’s a blinding fireball and an ear-splitting report, and it’s difficult to recover situational awareness, especially at my age, and even with my rail-mounted light. Civil? I don’t know how many have fired a 5.56 AR-15 carbine inside a room, but it’s sensory overload.
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