I've got a little first-hand experience with two Shield 45s and several full-size M&P45s. All have functioned perfectly. I've not noticed any particular ammo sensitivity with either gun. The Shields have surprised me with how well they have fed and handled some of the unusual ammunition I've tried in them. The full-size .45s have outshot similar full-size 9s and .40s so badly it makes you wonder what they are doing wrong with those guns. The Shield .45s are no slotches, too. I'm not overly fond of plastic guns in general but I can't find much fault with the M&P .45s - except for the triggers.