I just put a 300 AAC blk barrel on my cmmg upper and it worked at the in door range were the barrel was installed.OK, it worked 9 out of 11 shots. I've got three boxes of Remington 300 blk and it's hard to get your brass back in an indoor range.  I'll get to the range soon(out door) to check it out at 50 and maybe 100 yards. I'm waiting for my Foster dies and some brass I brought to get here. Does anyone know where I can get a case gage??? "O" yes, this is on a AR15 platform.
 Does anyone know were I can get a 6.x45 barrel for an AR15??? ok, and dies and case gage. I"ve tried wilson and Foster both and nether one has them. I've got a spare AR15 that needs a new caliber, I just don't have any use for a 5.56 caliber. I have two 6.8's(very accurate rifles, sub minute of angle at 100 yards) and now I have one 300 black out. but I think I need a 6.x45 now. I have all sorts of trading matieral, rifles and/or pistols. new and used.
 Pat

Check out spirit guns. They have the best 6x45's IMO, although they only sell complete rifles. Spirit Gun MFG

If you want a barrel or upper go to black hole weaponry. I got a barrel made from WOA because I am a brat.

I load 100g Sierra Spitzer Boattails to 2650 fps. Devastating on all game worth shooting in the south eastern US

they want way too much money, that's why I just buy barrels. I have two smith and wessons and one panther arms(DPMS) that are new in the box. all I need is a different barrel. and/or gas block
  Pat

I'm going with 6.5PCC... Black Hole Weaponry barrel and dies for $399 shipped.  6.5 is my choice in part because I have a 6.5 Creedmoor and have the projectiles.  Common projectiles for 308 and 300BLK is also cool.

Blackhole Weaponry for the 6 x 45 barrel. They are really reasonable on prices, and make a really nice barrel. Plenty of options for fluting if that kind of thing floats your boat and you can have the stainless black oxide finished if you like.

not sure on who makes dies

Redding makes the dies.

Be weary of fluting , its more for looks and weight reduction. It does not add accuracy. The material has to be stress releived before it can undergo fluting. Thats why a fluted barrel from Sabre Defense costs $600 and others are $300.