Found a little problem with the new gen 3 mags when used with Nordic Component .22 upper, so if you have the NC-22 upper and want to use the new BDM gen 3 mags, you might find this helpful:
Fine tuning the gen 3 mag for NC-22 upper
No issue when these gen 3 mags are used with Ciener-type conversion (tested with a Spike .22 upper).
Are you sure? We've a few of the gen 3 mags here in house, using our uppers on Cav Arms, Bushmaster and DPMS lowers and have no problems at all with fit or function.