Was at the NRA range yesterday firing my Springfield MILSPEC M1911A1 with a new Wilson 7 round magazine. Flawless feeding and extraction but the slide will not lock open after firing the last round. The slide DOES lock back with the factory magazine. Puzzled, I took the Wilson magazine and fired it through my Colt CCO -- no problem --slide consistently locks open when shot empty. Inserted the Wilson back into the Springfield and noticed that, if I push the Wilson mag further into the gun and keep it there by applying pressure, I can get the slide to lock open. Otherwise the slide stop does not engage. Duh. What to do? I suppose it is a problem with the M1911? Anyone have any solutions? Thanks.