Can’t get these damn guns to cycle subsonic rounds when suppressed. Even with the adjustable gas blocks all the way open the bolts barely budge, even with low mass carriers. I’m stumped. Suggestions?
This is why 300 blackout is soo popular. You are never going to get 6.8 or 308 top cycle 100% reliable with subs.
Use 308 subs in your bolt gun, and make your semi autos 300 BLK.
Why would a 300 blackout and a 308 perform any differently? Its the same bullet and theoretically in a subsonic round there would be the same amount of powder, or atleast force, pushing that bullet right?
Nope.
I’ll give more detail later when I have time.
No. Different BCG weights for starters. An AR15 and AR10 are vastly different in some critical aspects, but I’ll defer to Failure2Stop for specifics.
Forgot about carrier weight.
300blk seems to work well with pistol gas systems. Can you setup a 308 or 6.8 AR with a similar gas port location? Sorry, just thinking out loud!
There’s a balance between powder burn, port location, port size, and reciprocating mass.
You will not be able to get anything other than .300 Blk type factors to work with subsonic unsuppressed and supersonic suppressed without significant changes to the system.
The advice above is solid.
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But wait, I’m not trying to run subsonic unsuppressed. I’m trying to run subsonic rounds with a suppressor.
What 6.8 sub ammo are you trying?
What gas system and barrel length?
200+ grain projectiles with appropriate powder are known to work reliably in CAR gas barrels.
Ok, figured out the solution for the 6.8 at least. I have Bison Armory’s 11.5" Recon BSP barrel which is supposed to be made specifically for firing subsonic ammo but when read more carefully they specify a 200 grain bullet which of course only they sell. As for the .308, would a piston conversion be a possible solution?
I don’t know much about these cals, but 308 semis are setup to run on pressures l using a 165gr bullet at what, 3k fps? The same gas is used to push the bullet and cycle the action. You would need a very heavy bullet at a lower pressure to get to subsonic. Too low a pressure to cycle the action.
300blk is already a much lower pressure and lower velocity bullet. Getting to subsonic is not much different pressure than supersonic rounds. Thats why the gas ports are at the pistol location.
I don’t think a piston would help unless you rebuilt it to cycle at low pressure, but then full power rounds would likely beat the crap out of the gun.
The same issue exists with 223.