I pulled the barrel and started by determining how long to make to bolt. I measured with an adjustable depth micrometer (thanks Scotty!) from the front of the receiver ring to the rear of the front locking lugs and the rear of the rear safety lug so my new working dimension is the distance between the rear surfaces of the front and rear lugs. In my case I needed to shorten the bolt by .800"
For the most part I worked from the book The Mauser Bolt Actions, A Shop Guide by Jerry Kuhnhausen.
I decided to shorten the bolt by a method that is different from the book, this technique is to turn the extractor collar groove back by the ammount the bolt should be shortened and then part off at the back of the new groove.
Then counterbore the bolt body to a depth that maches the remaining bolt head length which is shorten length minus part off width, in this case .800" - .062" = .738" deep. The counterbore diameter is just a couple thousands over the diameter of the bolt head "stub" just cut off, you want a tight slip fit for a good solder joint.
Here's a picture of the two parts pushed together.
And here is how it looked before I started cutting.
Next is to weld on a new bent bolt handle. I chose the Leonard Brownell handle from Brownells, it looked like what I wanted and was cheap. Turns out it's a really nice handle that needs some grinding to remove the casting flash but has a really neat feature. On the stub end (where the weld goes) it has guide lines molded in on both sides at about 30 degrees to make it easy to grind off the correct angle for a nice fit on the bolt at the correct angle to clear a scope.
I made this welding fixture from scrap metal and a nut/bolt laying around the shop. If I thought I would do more of these conversions I would DEFINITELY invest in a "real" bolt welding jig, this is ugly and probably only fits this bolt/handle combo but it worked great for this operation.
Note the old handle used as setup for welder settings. I also turned a piece of brass to fit the inside of the bolt to act as a heat sink. Not pictured is the Brownells Heat Stop Paste that was piled on around the lug and lightly smeared all over to eliminate splatter from sticking to the bolt body.
The welded and semi-finished handle. In the right hand picture you can see the safety lug is kind of thin, I had to grind the front half off to clear the rear of the extractor as it rotates around the bolt. I would have preferred not to do it but the length was already established by the original owner and I didn't want to get into shortening the extractor, if that is even possible.
At this point I soldered the bolt head to the body. Since the joint was close to the locking lugs I decided to use soft solder to keep the heat down rather than silver solder, this was recommended by several folks and deemed strong enough to hold. We'll find out in the future. Again, lots of Heat Stop Paste and the heat sink and it turned out OK, now I have a one piece bolt w/handle and hot damn it fits the reciever!
Next shorten the firing pin by the amount the bolt was shortened. I ground a tool to match the original grooves in the firing pin, slightly tapered with radiused corners. Center drilled the back end and set up on a live center. The book recommends matching the groove dimensions (and spacing) of the original so that it fits the cocking piece/sear, so that's what I did. Then put the firing pin in the mill and cut the flats on both sides toward the front, lengthening by the amount to be shortened.
Cut the spring so the bolt can go back together. The picture shows the piece that was cut off that measures .800" long. IMPORTANT: It's not the OVERALL lenght that needs to be shortened but the COMPRESSED length that needs to be shortened so you can put the bolt back together. Measure the coil wire diameter, about .060", now divide the length to be shortened by the wire diameter and you get the number of turns to cut from the spring. By the way, there is no mention of this in the book.
Last step is to make the bolt face hold the .223 Remington case head which is much smaller than the original 8x57 head. Two methods are common; counterbore the face and install a bushing or solder in a ring of the appropriate diameter. I went with the easier method of soldering the ring, we'll see how it holds up over time. The picture shows the ring soldered in place and relieved at the bottom for the magazine feed. Notice that the ring crosses the ejector slot, I left that material there because if I cut it away there would be just a "point" on the bottom of the slot that would likely just break off and jam something up. The second picture is of the ejector and the notch to clear the ring. The notch is cut deep enough that it never contacts the ring from behind before the bolt hits the bolt stop, I figured the ejector would quickly break the ring loose from the face. The extractor is a blank from Brownells that I cut to fit the .223 extractor groove.
Now install the trigger to see if the bolt will fire.