All other things being equal, ammo costs not taken into consideration, what is better overall? I’m concerned with effective range, accuracy, and effect on target. I’m looking at a 8.5 300blk and a 12.5 7.62, same suppressor for either, griffin recce 7. Will also be using the same optics on either, so the round is the only variable.
Weight - win goes to 300blk
Full velocity rds - win to 308
Subsonic - draw, its a 308 bullet going at 1100fps or less. You might have issues with cycling 308.
I would think you’d have a lot of wasted powder in a SBR .308 whereas the .300 is optimized for it. Not to mention the longer receiver length, weight in a small package, and potential for cycling problems in the .308
Make sure the rifling twist is fast enough for subsonics if intending to use them. 300 Blackouts seem to have a 1:8" or faster twist. Most .308s are running 1:10" or so. So, the typical .308 running heavy subsonics may not sufficiently stabilize.
Gee, I have numerous firearms, both longguns and handguns and each one has a dedicated and/or practical purpose and I have a really hard time of coming up with a purpose for a .308 AR SBR from a civilian standpoint.
I would also be concerned with the effect that full power loads that were developed for a 24" barreled rifle would have on a suppressor when fired from a 12.5" barrel. Without a suppressor the muzzle blast would be hard to tolerate even with hearing protection. I’ve used a 10 3/4" barreled CAR-16 Commando in CQB and now I cannot hear thunder.
I have a 300-221 SBR AR (300BO, wildcat).
I moved the 308 suppressor to my AK 7.62x39
and M1A.
I had issues getting subsonic 308 and 7.62x39 to fly straight, I don’t think I ever got anything to cycle the guns.
When I was testing I couldn’t get subsonic rounds to expand/fragment. Assuming the bullet construction has improved with the 300BO and you can run it subsonic, I think that is the best round for what it does. If you have to go supersonic, then there is no reason not to gun up to 7.62x39. If I need to go with 308, it will not be subsonic or SBR. It will be for long range work.
I’ve considered going the SBR route on my current .308 AR build. I’m just looking to get more punch out of a 30 cal then I can get out of my 5.56. I want accuracy at short range (<300 yds) and would like the ability to fit in in a small carry case. Looking at both 12.5" and 16" Rainier Arms UltraMatch .308 Barrels. I still haven’t ruled it out, but if I was concerned more about running a suppressor, I’d just go .300BO. The .300 is only a bit better than a 5.56 and IMHO not worth getting into for normal shooting, but if I was going to run silent, (and I want to one day) it’s worth it.