I bought a MKIV series 70 Cogan Customized Colt in an estate deal and I haven't fired it yet, but when the slide release is pushed with the slide in the back position, the hammer will drop. It doesn't fall to the fire position, but stops about 1/8th of an inch from fire. The hammer doesn't stay cocked when the slide rams home. I'm pretty sure this is not normal and something is wrong, but since the gun has been worked on, I don't know. Any advice would be appreciated.