I have three .30 Rem AR magazines. They are DPMS magazines two are short I believe they hold 4-round mags, and one longer I believe it is a 7 or 9 round (not sure). I'd sell for $50 shipped or trade for three 6.5 Grendel / 6 ARC magazines (only interested in trading for 10 or 15 round mags).
I just got them for a buddy of mine. I like the cartridge, but remington designed it in a way where you can't even form it from a different cartridge, so I will just stick with the wssm ars.