Brownells Gunsmith Kinks® - July 2008
-- Mike Allen, MHA Custom in NC
I finally got the Colt together and test fired that I had to repair after cutting into the firing pin safety hole. I have installed many BMCS sights, a couple of which have been on series 80 Colts. Somehow on this one I had brain fade and forgot about the hole.
A common installation of the BMCS sight on 1911 style pistols is the low mount, milled-in installation in the forward or "protected" position. This installation works great on guns that do not have a firing pin safety. Recently I was reminded the hard way that this procedure will cut into the firing pin safety hole on a series 80 Colt leaving nothing for the spring to seat on. My solution wasn't easy, but it did save the slide. The bottom of the cut for the pocket that houses the BMCS blade is .150" below the bottom of the original rear dovetail. This cut removed quite a bit of the space needed for the firing pin safety plunger and spring. |
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The first step in the repair was to tap the existing hole 12-24 only a few threads in length(a finer thread would have been better but I didn't have a fine thread tap on hand). A 12-24 screw was then coated with #609 Loctite and screwed into the threads as tightly as possible and left until the Loctite cured. The screw was cut off and milled flush with the bottom of the BMCS cut on top of the slide. Then the slide was flipped upside down in the mill vise and a 3/16" carbide centercutting endmill was plunged into the hole until the there was only a .040" thick "disc" left of the screw I had just installed. Be very careful not to waller out the hole and make it's diameter oversized or you will find yourself also making an oversized O.D. plunger to fit in your new, oversized hole.
At this point the hole had a bottom again, but it was much too short for the plunger and spring. After some trial and error I found that by removing material from the top of the plunger I could shorten it to an overall length of .408" and still have a little bit of the spring recess remaining. Then 4 coils were cut from the spring and everything was reinstalled and amazingly it worked fine! I know this was a lot of trouble to go to for a safety that a lot of folks remove from their guns anyway, but nowadays it's not a good idea to disable any safety features.