These are used ProMag 32 mags for a Colt style 9mm AR. These don't work well with my MUTT but might work well for a factory gun? The last 15 rounds feed fine, the first five fail to feed every other round, and random fail to feeds until the last 15. It may just be that they need to be cleaned. Anyway I bought 10 of the Metalforms (ouch over $400) so I don't really need this anymore. At $8.33 per mag it's hard to go wrong even if you just use them for 15 rounders or to practice clearing a jambed gun. $50 or trade for 100 rounds of .357 Sig target ammo.