So far on my Lynx 12, factory mag had most side to side wobble, CSS Specs much less but still a little; MD arms 20 drum 0 side play, super tight going in, and a Magpul 15 drum very minimal side wobble. None of my aftermarket mags needed file fitting, CSS specs was the tightest fit locking in.
Bought 2 Lynx at same time, serial #s separated by about 300 units; both same fitment of same mags, bout same side play, and no file fitting required.
Factory mag cycled everything fine, 2-3/4", 3", buck, bird, slugs with the most wobble. Only other mag I've tried yet is promag 15 drum; ejects