Don't do this. I don't care who made it, it can cause problems like this. The firing pin stop is made to be thumped by the hammer, the back of the frame is not.Dropping the hammer with the slide off a few times as I did the initial field strip and cleaning caused a nasty burr that locked the frame up totally.
Pitting on the rails sounds like some form of rust or other corrosion. 4140 steel doesn't like moisture whether it was cast or forged. Just something to keep in mind, it's beneficial to keep them well oiled.