I wanted to get something done with the .45 conversion, so I figured I'd go ahead and get the bolt and carrier mostly finished over the holiday.
My first task was to open up the cup in the bolt to fit the head of the .45ACP case. I decided it would be easiest to open the cup to 0.500" with an end mill. The 0.500" cup will have just a little slop, but not too much.
With the 16" Thompson barrel, there is about 0.150" of case sticking out of the breech. The depth of the standard AK bolt cup is about 0.130". If the cup is milled much deeper than 0.150", the firing pin hole will start getting larger, as you will be cutting into the taper of the hole.
First, I clamped the stripped bolt in the vise. Because of the grooves in the bolt stem, I had to keep turning the bolt to get it to clamp evenly in the vise.
Once it was solid, I centered the firing pin hole with the mill head using a drill bit. I know there are tools for this, but I don't have one... I tweaked the position until the bit would go into the firing pin hole without dragging or flexing. I switched the mill on and ran the bit straight down to the shank. There was no drag and the bit went in without so much as a squeak.
I changed out the drill chuck and 1/2" collet for the 5/8" collet that fits the carbide end mill. I grabbed the 0.500" carbide 4-flute end mill and tightened it in the collet. I touched off on the bolt face to set for zero. A couple drops of cutting oil and the chips started flying.
The carbide mills are an absolute necessity when cutting the bolt, it's too hard for high speed steel. I took small cuts and used plenty of oil. The cut actually only took a couple of minutes.
I checked the depth and it was dead on, so I took the bolt out of the vise and cleaned it up for the test fit.
Well, I should have looked at the actual dimension on the cutter instead of what was printed on the plastic sleeve. The cutter was not the 1/2" cutter I assumed. It was actually a 17/32" cutter! The hole I milled wound up around 0.530", way too big for the .45 case. Damn. It may still be usable, but it pisses me off that I didn't check the cutter. This minor fiasco ruined my mood for the evening, so I cleaned up my mess and packed it in.
I may be able to use the bolt as-is, but it's a lot more play than I want. I could braze in a couple pieces of steel shim stock to take up some of the extra space. I may just use another bolt... Again, damn. At least I know how much trimming the extractor will need.