I have AR platform rifles in .223 and .308, as well as suppressors to go with them. First question I have is will the rifle cycle with a subsonic round? Second question is what kind of loads to use? I read in a American Rifleman magazine a few years ago, where you could use something like 9 grains of a pistol powder to achieve this. But I don't remember which powder and if that was for a .223 or .308. Any recipes for a subsonic load in either of those calibers?
Gas Guns will not cycle with subsonic rounds. They become a bolt gun at that point.
I believe Trailboss is the powder people are using ?
Originally Posted by kbaltrusch
There are some Wes, not a ton that is for sure. Definitely need an adjustable gas block though. And, you probably need to reload....that helps. A great suppressor helps also, all are not created equal.
A bastardized AR with super light springs and a light buffer can do it, but it is too mach of a pain to change stuff back and forth.
Build one that will work sometimes and leave it, or just shoot a 22LR Suppressed
There are some Wes, not a ton that is for sure. Definitely need an adjustable gas block though. And, you probably need to reload....
I wouldn't change back and forth. I would leave it. A lot of my stuff is dedicated for a certain task, but mostly specific fun.
Agreed!!
I don’t really have any loads in either so I can’t really answer the question you asked, but would like to see if you have come up with a suitable answer to your question. I have 30cal suppressors. Why not use your 223 lower and a 300blackout upper? You would still be sending a 30cal projectile down range at subsonic speeds getting very similar ballistics to the subsonic 308 and use your suppressor. There’s no changing springs or need for adjustable gas blocks and will cycle the action without hesitation. I have a sbr that I frequently switch between a 12” 223 upper and a 8” 300blackout upper. I’m thinking of adding a 18” 6.5 Grendal upper to the current pair to use as a “kit” type of setup. 300blackout for close range quiet work, 223 for medium distance work and 6.5 for anything that stretches out to about the most of my abilities.
Subsonic are a real hat trick when it comes to cycling an AR.
There are only a few powders that work in 300 BLK and the rifle can be finicky. CFE Black, A1680 and Blackout (Shooters World). Keep in mind the primary purpose of 300 BLK was to shoot a 220gr pill subsonic. It shows you how finicky this can be. It’s a balancing act of having a powder slow enough that the gas pressure is high enough at the port (~15kpsi) to cycle the gun but fast enough to actually burn.
Then there’s having a rifle with a fast enough twist to stabilize the projectile at a subsonic velocity. So you can go with a heavier projectile but then it keyholes because it’s moving too slow and the twist rate isn’t fast enough to stabilize it.
I don’t think I have ever seen a 5.56 subsonic cycle a gun. Doesn’t mean someone somewhere hasn’t don’t it, it’s just not an easy task. Then there’s an issue with a 90 grain bullet having about the same muzzle energy as a 380 ACP.
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