Re: 30 Remington AR
Jense Precision has already built and tested several 30 caliber AR-15's base on necked up 6.5 Grendel brass. It shoots extremely well and is very accurate when loaded appropriately.
My knowledge is first hand. I "spec-ed out" and tested the first two ".30 AR-15" rifles. I did all the funding, testing, trouble shooting and insured reliability on the rifles.
The first barrel is a lightweight 16" barrel used on a quick barrel change system pictured on the Jense Precision website. Reliable, light and .30 caliber deadly.
The second rifle is a Bull Barrel match version of the first with a very precise 1:10 twist. This barrel was specifically designed to shoot 220 and 240 SMK's subsonically. It's an amazing rifle that can blast out 110 grain V-Max's for varmint or deer hunting or shoot 240 SMK's subsonically whisper quiet.
The Hornady 150 grain FMJ bullets shot the best for "everyday inexpensive shooting" and overall did amazingly well. The Hornady 150 FMJ's are not only accurate but also had some of the best penetration I've seen in a .30 caliber in a long time. For every day use, the USGI type 147 grain full metal jacket bullets are also good to go.
The reamers for the ".30 AR-15" (later re-named 30BPC) are available from David Kiff at Pacific Tool and Guage. You need to specify either the bolt gun "match" reamer or the Gas Gun reamer when ordering.
Jense Precision is experienced and excellent at building and testing the .30 AR-15. For those interested, I'd start with Jense Precision first.
http://jenseprecision.com/