I gave up on the PCV Beowulf mags myself... Too much flex in the polymer body and they failled in competition a few too many times. Nothing like a $2500 rifle debilitated by a crap mag.
I run nothing but AA metal myself, but I've quit bringing them in as the cheaper crimped ones are allegedly due to hit the ground any day now. Bunch of sponsor sites have them for $39.95: hical, SFRC, Dominion Outdoors, Hoplite Tactical, not sure who else.
I strongly encourage you don't waste your money on plastic and go to metal...