Castandblast,
Son of gael answered your question on the ar mag confines. I just meant the short msg length of 2.26 or less which sounds like yours is when a little shorter. Not to big of a deal. The RMR bullets I referred to are Rocky mountain reloading which makes their own brand of the 69 and 75 bthp.
I would think most of those bullets made for the ar magazines would work as well as most of the weights falling in the 60s. I think the 53 grain vmax would also be a good one
