does it use 5.56 mags, or need special magazines?
The 6mm ARC uses special Grendel magazines. The case is too fat for 223 magazines. There are some good options.
Brand recommendations, please!
Kaiser Norton
I'd try ASC mags as well. I use them for my 6WOA. They work very well... I also use another brand, but can't think of it at the moment... These are steel mags and I've never had any problems with them..