Perhaps the biggest obstacle to carrying a full sized 1911 concealed is the sharp edge at the bottom of the frame where it meets the mainspring housing. Some smiths will round off the corner to get rid of the sharp edge. Ed Brown makes a Bobtail conversion main spring housing (MSH) that requires modification of the frame to create a smooth profile.
You’ll notice the Bobtail MSH has quite a bit of material removed from the bottom of the MSH. This is accomplished by using a Officer’s ACP sized main spring.
Ed Brown sells an installation fixture. A bobtail conversion can be accomplished without a fixture, however, use of one makes things easier. I have a couple of friends who use these fixtures on bench top drill presses with great results. To align the fixture, I install it into the vise and pass the drill bit through the location of the new hole.
The frame is then secured in place with the factory main spring pin. At this point it is advisable to run a dial indicator along the y-axis to make sure the frame is level.
The new hole is spotted with a #2 center drill.
Finally I drill the hole. Brown recommends drilling the hole from both sides, in two steps, checking to make sure everything is aligned- that is some solid advice. I machine things all the time, so I just did it in one pass.
I drilled the hole .001″ undersized. I use a hand held 1911 reamer from Brownells to make the hole the proper size.
This is what the new bobtail MSH looks like now. Note the material I have to remove from the corner of the frame. Also note that the back of the MSH sits above the frame, since I am coating this gun I’ll end up blending that in.
I like to live on the edge. That means a belt grinder with an aggressive grit (heats the parts less than a fine belt). The downside of this method is you can destroy a frame. Files and abrasive cloth are the prudent choice.
I don’t get too crazy on the belt grinder. At about this point, I move back to the bench with some files and abrasive cloth.
The Bobtail is coming along well!