AR project caliber

[barrowsr]

Not sure if this is the right forum. I'm planning a black rifle build and want something larger than a 223/5.56 to fit in an AR15 platform. I found a great article on the 6mmAR based on the 6.5 Grendle case but that build had a few cost and compatibility issues. Since I don't need the last shred of velocity from this target/dog gun I was thinking about just using the 6mmBR as is. As long as the OAL stays within the required magazine length I would think the added neck length would be an advantage in a semi-auto gun. Am I ignoring any problems this idea may incur?

Thanks
Robin

 

[jonbearman]

Why not the 6.5 grendel? It is accurate and doesnt beat you up.

 

[barrowsr]

Thanks,

The 6.5 Grendel is a candidate but if I understand it's history there are 4 different versions out there.

 

[mac86951]

Add to the fire, the Grendel is the one for longer ranges and larger case volumes.
I've seen some Grendel rifles can be picky, but usually a sound set-up is not a problem.

6mmAR being grendel based and thus will have similar potential issues

-Mac

 

[akajun]

6 hagar

 

[redlabel12ga]

6x45

 

[spclark]

Personally I'd stay away from 0.475" dia. 308-size variants like 6BR. Some get it to work but not many out of those I've seen, especially when NRA-style rapid-fire gets going. Besides there's not much steel left around the chamber / bolt lugs.

For the NRA match & mid-range stuff I do I chose the 6HAGAR. Works great out to 600 yards w/ 105-grain bullets in a 26" barrel. Early drawback was brass (you had to make your own from 30REM) but Hornady's making it now, Creedmoor's (and a select few others) sell it & it's superb stuff.

I messed with two 6.5 Grendel match uppers (and a bolt gun barrel) for a few years. Left it behind after recurring reliability issues, mostly mag-related. I know 6mmAR / 6RAT shooters who seem to be making them work OK. In the bolt gun it worked OK but past 600 yards the lack of case capacity is a disadvantage when any bullet heavier than ~ 120 grain gets loaded.

6x45 has its adherents but with the larger bore and heavier bullets the limited powder capacity caps your effective range over a 223REM in a manner similar to that of the 6.5 Grendel.

John Holliger's (White Oak Precision) 6WOA works very well too, uses 6.8SPC brass necked down to 6mm. Not quite as long a case as the 6HAGAR it's a little compromised for powder capacity for 600 yards but that's irrelevant at shorter distances or with lighter bullets than the 105's most use at 600.

 

[barrowsr]

Thanks to all for the suggestions especially spclark for the detailed response.

 

[barrowsr]

Thanks but I want to stick with AR platforms. I have two lower receivers for project guns and this will be one of them.

 

[jscandale]

I have been using the .220 Thunderbolt. With 29-30 grs of powder behind the inherently accurate .22 cal bullets, it's hard to beat it in the AR platform.

JS