it sounds like what you shot was a pistol scope. Was it also mounted on a semi auto? Typically I've seen this done via a frame mount that comes up and over the slide. Adding all that weight to the slide can impede function and it's probably just harder on the scope.
But, I could be wrong, I've not seen any kind of magnified sight that's installed directly to the slide of a 1911
But, I could be wrong, I've not seen any kind of magnified sight that's installed directly to the slide of a 1911