Finally had time to work on this again today. Another close inspection of the bolt under a magnifying glass (cause I'm getting old) revealed burrs on every single edge and corner of the entire bolt. I suspect that the fail-to-fires that I was having before were caused by some of these burrs. The extractor had burrs all around the round "top" of it, and that may have been hanging on the rim occasionally and not letting the bolt close completely. The other burrs all around the bolt may have been dragging just enough to contribute to the problem as well.
I used a little grinding rod in the Dremel to round over that rail that goes through the magazine some more. I got it shaped like the gap in the mags now. It's not a square peg going through a round hole anymore. I deburred every edge, corner, nook and cranny over the entire bolt with needle files. I polished those areas with various Dremel fiber polishing pads and polishing compound.
Phil, one thing that I'd suggest you consider is to leave the bolt unfinished unless you plan to increase your price enough to allow you to deburr and polish the bolts before finishing and shipping them. I had to file and polish away a good bit of the finish in order to get everything smoothed up. Might as well just leave it bare metal, and then folks could have it blued after they get it cleaned up and working (if they didn't want it to stay bare).
I took the gun to the range after hand cycling a few mags worth of ammo successfully. At the range, I went through the first mag without a hitch until the 9th round. It fed and fired just fine, but the bolt hung open. I looked and saw that the extractor had come out and was hunging things up. The extractor spring was bent a little on one end in the process.
I didn't bring all my tools, so I just put all the pieces in my pocket and continued shooting the gun without the extractor. I got about 60-70% stovepipes without the extractor, but that wasn't a surprise. In 100 rounds or so, I got just a few FTFs. Some of them were probably due to the bolt not getting closed well enough after clearing a stovepipe. I don't know how many FTFs I would have gotten, if any, if the extractor hadn't come out.
When I got back home, I took it all back apart to replace the extractor. I turned the spring around and put the little plunger piece onto the bent end of the spring. It fit on very snug, and it forced the spring to straighten out. It seems to be good to go. While I had the extractor out, I took the opportunity to deburr the rest of the extractor as well as the slot in the bolt where the extractor goes. I don't know if those burrs were what caused it to come loose or not, but I figure it may have had something to do with it.
Before replacing the extractor, I also took the opportunity to polish the bolt face and case pocket. I ground down a dremel polishing wheel so that it would fit down into the pocket. I worked the entire bolt face over good with polishing compound until I got a shiny mirror finish. There are a few grooves in the pocket face that would require a lot of filing to get rid of, but other than that it is shiny and slick now. I polished and compounded some more on the rest of the bolt while I was at it. To get the entire bolt slick, I had to remove most of the finish. I decided I'd rather have the gun function well instead of leaving the finish intact.
It is SLICK now, and hand cycling the bolt after reassembling everything felt really smooth. Before today's work, it always felt like there was sand in the action even though it was clean and lubricated. I think I probably have it close to where it needs to be now. I can't test fire it anymore just yet though. The buffer was just about chewed up when I took it apart - after about 120 rounds total fired. I deburred the buffer holes in the receiver some more in hopes of rounding the edges enough to keep a new buffer from getting chewed up so fast.
Do I need more main spring coils to keep from pounding on the buffer so hard? Do I need a different buffer material?
I'll get some new buffers and go shoot it some more, hoping the extractor stays in this time. Any tricks for keeping the extractor from coming loose?