OK, got it.
Thanks for the clarification.

The lack of power comes from not getting all the powder to burn, the spin just makes the bullet stable.

I think my 7.5 is a 1 in 7 twist, it doesn't keyhole

I'd add to that: using a red dot sight.

I wouldn't agree that those groups with that ammo demonstrate the mechanical accuracy capabilities of the barrel. Barrel length, number of rotations before exiting the barrel, have little effect on accuracy. The major factor that comes from a short barrel is lack of and loss of velocity. At realistic ranges for the 5.56 cartridge the bullet won't drop below supersonic velocity, which is where it would become unstable.
A short, rigid, high quality barrel will likely be more accurate than a long, whippy, lesser quality barrel.


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I'd be going with a 10.5" and 300blk Out.

I have a BHW 10.5" .223 Wylde 1:8 heavy profile barrel that is more accurate than either of my 16" 1:7 barrels with both 55gr and 62gr. Maybe my 16" barrels are just inferior quality, but I've been very impressed by the 10.5" barrel. I had low expectations of accuracy going into it, but now that I've seen what it can do, I'm sold.

Dan, I'd take a look at Black Hole Weaponry (now Columbia River Arms) or Ballistic Advantage.

My 300 is a 8.5" and 1:8. I only shoot it with subsonic ammo and a suppressor.

My 5.56 SBR is 10" and 1:7. I bought it as a complete upper from DSG, I'm not sure where they get their barrels. It has a thinner profile under the hand guard. Haven't put it on paper but i'm hitting an 8" gong from ~70 yards out with an MRO and 5.56 nato.

I didn't intend to build a 5.56 SBR. When I was shopping for the hand guard for my 300 SBR I came across a deal on the complete upper.

Also check out http://www.gmriflebarrel.com/ or http://pac-nor.com/ for off the shelf stuff.
I also have a buddy, https://www.instagram.com/blackmagicgunworks/ that does some nice barrel work, though he is out of state.

I'm curious if that accuracy difference might be twist rate. In either case, im checking BHW out and seeing if my buddy is a direct dealer for them still.

should have done 10.3/5 for both

Dan, next time we're at RFGC for the black rifle, bring you lower and you can put my 10.5 upper on it and run it to see what you think.




Ric

I finally got my Form 1 approved for a 10.5" barrel on a 5.56 SBR that I am converting from a S&W M&P 15 Tactical lower. I was going to build a 300 BO SBR too but due to issue with serial # on the lower being screwed up (thank you Spike's ) I did not make it in before 41p rule change. Besides, as I am using the 300 BO for hunting I want a longer barrel anyway.

Any recommendations? I was thinking about Tacoma Surplus Ammo and Arms' complete uppers as the prices seemed good, but didn't know much about them.
http://www.surplusammo.com/categories/a ... ppers.html

AAC says 8.5 is optimal for subsonic 300 bo.
I have an 8.5 rainer arms match barrel on mine.

SAA

Aero Precision or Ballistic Advantage

Also, you really only need one SBR lower. Just use separate uppers when you want to change between 5.56 and .300 BLK (but don't mix up your mags!). The .300 BLK upper can be 10.5" or longer...it doesn't really matter as long as you retain the 5.56 upper in the original (registered) configuration listed on your Form 1.

Are you going to hunt with that?

No. I'm not a hunter. I do have a saker 762 can on it though.