having a simular issue as well
i gues i spoke too soon. just got my sig 1911r in on thursday purchased 8 mags with it all from sig. went to the range when i picked it up , shot like a dream, very accurate no feed problems but 8 out of 10 times would not lock back when the mag was empty. went and tried my brothers kimber mags in the gun locked back 100%, used those mags in his gun and his locked back every time as well. leaving me a little baffled. so now i have loaded 2 mags for a couple days and plan to head to the range tomorrow with my fingers crossed and hope that makes some minute difference. so has anyone else ever experienced this issue?