Quote Originally Posted by cofi View Post
you can run 15/22 mags without this adapter in the 22 conversions
Also, without an adapter or something to shim the 15-22 mags, they'll lock into a regular magwell and function, but they'll be loose. S&W made the magwell of the 15-22 smaller than a standard AR magwell, and made the 15-22 mags shorter by 2mm, front-to-back, to fit.