basic Metalform mags work well. At one time you could pick them up cheaply from outfits like CDNN; that particular outlet is so busy they've suspended online ordering.
Mark

Brownells seems to have plenty in stock, offer a decent C&R-holder discount, and ship quickly.

My son is a little shy on CMC - only one he bought fell apart before he got through a box of shells. They were good on replacing it but had to pay to ship the junk one back on our dime.