I had problems with my Tikka 223 feeding 77's in the original Tikka mags. I replaced the floor plate with one compatible with AI and/or MDT mags. Have to trim slightly the bottom of the receiver for the AI mags to fit up in there correctly, but it was no big deal. (you can also trim some off the top of the mags lips if you don't want to touch the receiver). (if you use MDT mags there is no need to modify the receiver and/or magazine).It feeds and runs like a champ now with 77's.