You know me. I don't want to be bothered with cleaning brass, FL sizing, using case lube, trimming, none of that crap. For the AR, if I can't buy it by the thousand, cheap, already sized and deprimed so all I have to do is seat a primer, dump powder, stuff a bullet, shoot it and leave the brass where it lands, I don't want to mess with it.
For me, the AR is a low performance platform that fills a niche pretty nicely. Tons of fun! Start introducing all the stuff in that first paragraph and I'm not so sure I'd be having so much fun with it anymore.
I don't see turning the rims as much of a hurdle though.
If I'm reading you right though, and maybe I'm not, but it sounds like you would need a magazine specific to the BR case? They exist, at least, it sounds like? Or no?
You really ought to do it. Wouldn't be any big whup to get that cutting head made. Heck, Butch Lambert would probably sell you one. I have a couple friends with lathes, or get a HF lathe to do your own. I imagine with some careful setup you could hold runout to +/- a tenth or two which an AR is never going to know the difference.
- DAA