I'm building an SBR once form 1 submissions are open again and I was thinking of going 300 BLK since I wanted a <8" barrel. I won't be suppressing it anytime soon, should I just stick with 5.56?

I've got a 300 blk pistol, that I'm in the process of suppressing and will be getting a SBR lower for it soon. 300 blk works great woth an 8.5" barrel.

First know that the ideal barrel length for powder burn with the 300BLK round is 8-9". Less than 8" works but not ideal.

Running a 300BLK rifle unsuppressed but with subsonic ammo will still be quieter than 5.56. I assume you plan on eventually getting a suppressor for it?

Eventually, maybe in the next 3-6 months

Also keep in mind that many suppressors have minimum barrel length requirements or you aren't covered if something goes wrong (presuming the suppressor company offers a warranty).

Good thing to point out. Also keep in mind this rating can change with supersonic vs. subsonic ammo on some suppressors. For example most pistol suppressors are rated for subsonic only with 300BLK.

Right...also good to remember!

That's an easy one, do both. When you do a form one for an SBR on an AR platform you do have to set it up in one caliber. But, you can switch uppers also as you like. I have two 300 Blackout uppers set up for AR Pistol/SBR and 3 Uppers in .223 AR Pistol/SBR. Basically I have lengths for suppressed and non-suppressed in each caliber.

If you want a 8" barreled pistol or sbr, go with 300blk, the ballistics are way superior to 556... I just did a crap ton of research on this the last few weeks

Most of the time I've seen 8.5 300 barrels, they allow all the powder to be burnt off.

Thanks for the advice. I'll go with 8.5 and plan for a can in the future

does that 1/2" make that much of a difference? on the 300blk forums, most of them go 8", which is why I thought to go that route.

also, I thought with a heavy grain 300blk on an 8" barrel, the round is automatically subsonic? I've got lots to learn with 300blk...

8-9" is good to go. The powder is also really important especially with semi-auto. Wrong powder and you won't achieve subsonic and properly cycle the action. AA1680 is one of the best but can be hard to find.

I have been playing with a 7" 300blk barrel from DSA. It is running supers just fine, sub unsupressed was not cycling, but that's hardly a mystery. (add can, try again)

I havent seen AA1680 locally but its pretty available online. Powdervalleyinc has it in stock. AA5744 is a decent alternative but thats a stick powder but it pretty much same burn rate and performance as 1680 (in my experience)