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Sub Sonic 223 loads

Aloharover

Aloharover

Gun Builder
Joined
Jan 1, 2021
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3257
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Some of you may remember the Double Star low buck 11" SBR I built back in 2007. Well 15000 rounds on its still running great. Still running the original DS BCG and YHM Phantom can. Contrary to all the arfcommers that said it was crap parts and would blow up in my face.

Anyway, I am going to swap out the low profile gas block with an adjustable regulator. And want to try some subs with it.
I have been using adjustables on a couple other rifles like my 18" WOA DMR. Really like being able to dial in to a specific hand load.

But I have never tried subsonics in a 223 AR.

I want to use 77 smks for the bullet, LC brass CCI primers.

I was thinking a heavy bullet is easier to go slow with, but I worry an SMK going 1000fps will just tumble instead of fly.

Not sure on powder, type, amount, etc. I am thinking a pistol powder is best, but again just not sure.

So is anyone doing subs out of a suppressed SBR AR?
 
You might be right about getting a 77 to stabilize with both low velocity and short barrel.

I use the Hornady 75g Interlock (2300fps) in my 10.5" piston pistol, with Surefire can, and it's not hearing safe, but I think it would be quiet enough to not cause major hearing damage if shot inside.
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Not sure of the muzzle velocity of my so-called "subs" but I am, too, running a 11.5" 1/9 generic non chromed barrel sbr also with a Phantom. I do know that with 55gr BTSP projectiles and 16gr of 4064 powder the bullet does not tumble at all. Any less of a charge and the gun begins to short stroke and fails to strip a round from the mag. In my "experiments" I went as low as 12gr of 4064 and other than cycling issues nothing ever tumbled. Damn near whisper quiet with 16gr, though. I am more concerned with the gun still cycling than the utmost quietishness. I really never considered using a pistol powder, however. I do have a bunch of 4227 I use for my magnum loads (.357, .44), grab a Ti skelentonized bolt carrier and lightweight recoil/ hammer springs... the mind whirls...
 
Come over to the dark side and rebarrel to 300blk. You can toss 220gr subs long time joe.
 
I use 68gr BTSP over 4.6 grains of trail boss. It will chrono in the 1050-1150 range. No key holing on the target at 25 yards. Will get out to 100 yards have never tested it past that range.

This in a regular 16 inch barrelled AR15 with a gemtech one suppressor. Quieter than a pellet rifle. Will not cycle though next round though.
 
USMC Gunny said:
I use 68gr BTSP over 4.6 grains of trail boss. It will chrono in the 1050-1150 range. No key holing on the target at 25 yards. Will get out to 100 yards have never tested it past that range.

This in a regular 16 inch barrelled AR15 with a gemtech one suppressor. Quieter than a pellet rifle. Will not cycle though next round though.
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Thanks. I am hoping the adjustable gas block helps with the cycling
 
I guess my big concern is going too low and getting a bullet stuck in the barrel
 
Aloharover said:
Thanks. I am hoping the adjustable gas block helps with the cycling
Click to expand...
Not too sure an adjustable gas block will make any difference on the low side of a powder charge. To cycle with a very low powder charge one might have to really open up the gas port drilled in the barrel (i.e., the opening in the barrel is the limiting factor for gas flow, you can reduce the gas to the BCG with an adjustable gas block but you can't increase it any more than the gas port in the barrel will flow. And AR's need greater amounts of gas than, say, a Mini-14 to cycle properly). I suppose if the gas opening is increased for a diminished charge then an adjustable gas block would be critical for a standard ball load.
 
Do I need to add something to the case since it isnt full of powder?
 
I don't but it wouldn't be a "bad" idea. Something like beeswax, perhaps...
 
Aloharover said:
Do I need to add something to the case since it isnt full of powder?
Click to expand...
Trail Boss would probably work, and fill the case with a minimum weight.

I haven’t messed with SS 5.56, but 13.0 Grains of TB almost fills a 308 case and gets me 1050 fps with a 220 SMK. I feel like when I was researching, Hogdon had a .223/5.56 Trail Boss SS load. Problem is, these days, you’ll probably have to pay gunbroker prices.
 
Aloharover said:
Do I need to add something to the case since it isnt full of powder?
Click to expand...
I've heard of using a cotton ball to hold real light loads into the rear of large cases, but that's probably from someone loading tiny loads in 45-70 or 300wm
Can't imagine that any part of a .223 case would be able to hide from a small rifle primer.
 
Good to see you back, Aloharover!

Black powder 45-70s and other large loads used corn meal or grits as a filler for loads. Not sure WTF that means for current loads but it may be better than cotton balls.
 
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