The Wilson is a 0.200 as well, which means that the Colt had minimum holes in the frame. I've never seen that, but it is commonly reported. I bought a 0.201 reamer that I've used to clean up the entry hole on guns with undersize pins. Of course, it's usually better to "fit the part to the frame, not the frame to the part", but if plug gages are available, pin holes can safely be reamed to spec. EGW sells a 0.203 slide stop for cases where the hole is oversize.Just to follow up, I helped a friend fit a Wilson slide stop on his Colt and it was just oversized that I did have to turn down the pin a little so that it would rotate freely enough, otherwise similar to your case, it would not lock the slide back.