I have mine in an Ati Stock aswell, i have 3 tapco mags, started with one till i got it to fit and cycle dummy rounds properly, then got the other two and had them done in 20 mins with a dremmel. When you smack the unmodded mag into the magwell, then all the pinch points are evident, file down and voila. The ati magwell needed some filing and dremmeling as well to make room for the wider mags, not a big issue, not worth spending the extra money on the tapco. unless you just want options..