10" + on a 5.56 barrel will get you almost certain good performance with decent ammo. With less penetration than 9mm. with a nominal size difference (I can't imaging why anyone wants 7" 5.56) I know nothing of .300.

Seems like there are some great bullet options in supersonic loads.

Can anyone give their opinion of the difference in sound levels between 223/556 and 300 BO in pistol configurations?

quote:

Originally posted by Sourkraut:
Can anyone give their opinion of the difference in sound levels between 223/556 and 300 BO in pistol configurations?

Short answer -- both are really loud and unpleasant.

The best answer would be measuring the noise of comparable barrels, comparable ammo, in multiple locations with quality decibel meters.

To my plug- and muff-protected ears they're pretty similar. Maybe a touch louder with the 223, but that could be pitch/frequency issue. Both burn about the same amount of powder, both send bullets at supersonic velocities, both are almost certainly achieving incomplete powder burn in the short barrel. Although the 300blk likely burns powder a little better, due to the larger bore volume and greater gas expansion capabilities within the bore.

I shoot suppressed and wear at least one level of ear pro. My 11.3" 300blk is noticeably louder to me than either my 14.5" or 16" 223 AR-15s. Not apples to apples, but I can guarantee that a 300blk SBR is a loud gun.

Fritz, the 300 BO uses pistol powder which is faster burning. I would think it is more efficient at burning up powder in shorter barrels than the 223?

I agree though, a blackout SBR is very loud. I shoot all mine supppressed so not an issue for me.

Thanks gentlemen! Sounds like a another suppressor in my future. Suggestions?

When I was doing my research on what caliber AR pistol to build it seemed that the general consensus was that once you get under 10.5 inches, the .300blk is better than 9mm and 5.56 calibers.

I've also read that 6.5 Grendel outperforms 5.56 at an length of barrel. It's great out of longer barrels but apparently doesn't suffer as much as other rounds do once you shorten up the barrel.

quote:

Originally posted by Sourkraut:
Thanks gentlemen! Sounds like a another suppressor in my future. Suggestions?

SiCo Omega with a Keymo mount from Dead Air.

quote:

Originally posted by Scurvy:
When I was doing my research on what caliber AR pistol to build it seemed that the general consensus was that once you get under 10.5 inches, the .300blk is better than 9mm and 5.56 calibers.

I've also read that 6.5 Grendel outperforms 5.56 at an length of barrel. It's great out of longer barrels but apparently doesn't suffer as much as other rounds do once you shorten up the barrel.

Truth.

Only disadvantage of the 6.5 is cost and a bit of recoil and perhaps a slightly more fragile bolt.

quote:

Originally posted by Sourkraut:
Strambo, how long is the barrel on your Blackout?

My Blackout is an 8.5” pistol. My HD AR however is a 10.5” 5.56 SBR with 62g Fed. Fusion ammo.

Let me throw 6.8 SPC into the mix. Obnoxiously loud, but incredible ballistics out of short barrels.

11.5 (more reliable and bolts last longer). Under 11.5, a 300 blackout first then maybe a 10mm.

This message has been edited. Last edited by: Biggy,