For my Colt C.C.O. with Officer's-size butt, I use the 7-rounders supplied by Colt (made by McCormick). For back-up mags, I use the McCormick 8-rounders with the accessory Officer's base pad that prevents over-insertion in the shorter butt. They all work 100%.
As mentioned, standard-length Government Model mags (with no over-travel pad) may bind up the gun if inserted too vigorously, but should function properly if eased in.
Steve