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). Use a cutting wheel (and safety glasses). Don’t fight it! Sometimes this is necessary to ensure function. 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 gas expands behind the bullet traveling down the barrel’s bore, increasingly greater volume is available for the gas to occupy, and 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 that 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. Supersonic would totally overstress this system. This is a 4-inch port location on a 16-inch barrel. A pistol-length gas system has been, for me, a key to getting fresh-off-the-workbench reliable function from subsonic Blackout. 30-caliber bullet gets put to work effectively because the pressure at the gas port is higher. Done like that, the relatively tiny amount of fast-burning propellant behind that honking. Run a pistol-length location gas port (4 inches ahead of the chamber area) with a carbine-length (16 inch) barrel. I have found that the best overall approach to subsonic function is to shorten gas system length. 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, without modifications having been made to the gun. It works! Subsonic Architectureįirst, I’m always willing to risk boring knowledgeable readers with basic information, because it’s important to start at the start. Two Blackout barrels: carbine port location on the stainless pistol port location on the other. A 12 gauge slug, on the other hand, over-penetrates. Any bullet that’s built to either fragment or readily expand (not the same things but about the same effect) isn’t going to get far after it meets a solid object. This is really all about bullet design and bullet engineering. 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. Just a bit about the whole “defensive-rifle debate”: Some say something like, “5.56 is not a good choice for home defense.” I agree, but not for some reasons commonly given. (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. 300 Blackout is plenty powerful, in my estimation, and with radically better shootability than a higher-pressure carbine loading. Most subsonic Blackout ammo uses a bullet in the 200-grain range, and, of course. That’s another debate for others to work though 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. 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. Good stuff.Ĭivil? I don’t know how many have fired a 5.56 AR-15 carbine inside a room, but it’s sensory overload.
Big bullet! My magazines currently hold my most-trusted Nosler 220-grain factory ammo. I built a specialty AR-15 for home defense that I also featured in recent book project, and that was my choice. One reason for its popularity is the supersonic/subsonic option. Pretty much, it’s for those who want a bigger bullet in an AR-15 with a minimum of technical distractions (some call them problems). I like it especially in the shorter guns, and, around here at least, it’s looked on as an effective Whitetail cartridge choice. 300 Blackout, aka: AAC, is a popular cartridge among AR-15 fans.
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