Subsonic .308 load that cycles in AR-10?

LRSHOOTER0311

Green Eyed Devil
Belligerents
Minuteman
Feb 7, 2018
245
50
34
Anyone cracked the code on a Subsonic .308 load that cycles reliably in an AR-10 with an adjustable gas block?

I have seen the Atomic Ammunition, but I don't think it will stabilize in my Daniel Defense 16" .308 AR-10, after running it through Berger's stability calculator.

I have heard of using Bulky Powders, such as:
  • Accurate Arms 5744
  • Trail Boss
  • N32 Tin Star
The N32 Tin Star can give a 95% fill with a starting load of 15.5 gr and give about 1,332 FPS but to get down to 1,050, the pressures drop too much. Wondering if a gas block could help.

Projectiles I have heard everything from:
  • Lead Cast
  • Lead Cast Hi-Tek Polymer coated
  • Leihgh Defense
Wondering about weight and specific type.

Primers are question too....

Interested to hear results or load combinations that worked.
 
Last edited:

Gunfighter14e2

Rusty Nail
Banned !
Belligerents
Jul 9, 2002
7,948
10,749
219
Alabama
eHam.net
It has been done but if you try to shoot a highspeed w/o changing it back, BCG, Buffer & spring combo, an closing up the gas post your going to have a very bad day.

There is far more to making one operate in semi than most know. You can get the bolt back no problem, with reduced carrier weight an spring rates but now, it does not have enough ass to strip a round from even a 5 rd mag let alone a 20. In order to get it to strip rds it has to have enough ass going forward as well.
 

GBMaryland

Sergeant
Belligerents
Feb 24, 2008
1,327
1,214
219
Maryland, US
Hey man, I picked up some sub sonic 308 rounds from Lehigh bullets.

cycles my A.R. 10 with an adjustable gas block and a suppressor on it, but I did have to change the sping.
 

LRSHOOTER0311

Green Eyed Devil
Belligerents
Minuteman
Feb 7, 2018
245
50
34
Hey man, I picked up some sub sonic 308 rounds from Lehigh bullets.

cycles my A.R. 10 with an adjustable gas block and a suppressor on it, but I did have to change the sping.
Send me a link to the rounds and the details on the spring swap.
 

GBMaryland

Sergeant
Belligerents
Feb 24, 2008
1,327
1,214
219
Maryland, US
to be honest, I don’t remember trying it with 20 round mags.

i’ve been using 10 round mags, but I might assume they’ll be a similar amount of pressure on the bottom of the bolt carrier.
 

LRSHOOTER0311

Green Eyed Devil
Belligerents
Minuteman
Feb 7, 2018
245
50
34
Let me see what I can find… I might even have some spare parts that you could have. Looking at Lehigh defense, it doesn’t look like they have a lot of stuff in stock at the moment
Thanks! I appreciate the help.
 

1jonathan1994

Sergeant of the Hide
Hessian
Belligerents
Minuteman
Feb 21, 2018
138
15
22
Laurel, MS
I got a 18in rifle gas system to cycle 125s at 1800 fps, but the brass was not expanding to seal the chamber. This could lead to a bad day. Chamber didn't seal until 2400 fps with exterminator and 4895.
Aluminum bolt carrier is your friend. Also super weak buffer spring, cut the ejection spring shorter, and remove all but one extraction spring. Polish everything. Pmag helps too.
Car gas with 16in? Maybe drill gas Port out
FWIW 300 blackout already does what you ask.
Twist rate will definitely kill your concept.