As promised, here is the followup.
I should mentioned that this gun is almost new. Originally, it jammed constantly with 333's. Then it slowly got better until it about 1 out of 3 shots jammed. So it seemed to be wearing in.
I ran a number of test cartridge through the feeding system (cycling the bolt) as I went along to check for function. The first test cartridges came back with some variations, always with a dent right on the front face of the bullet, and also with scuffing along the .22 diameter section and transition areas of the bullet. But I never got it to jam, either with test firing or with cycling. I am convinced that the dent on the front face was what sometimes caused the jams with the gun.
Feeding the bullet by hand into the chamber mimicking the angles it actually sees, I could easily get the bullet to catch on the chamber edge.
The photo below shows the feed path of the 333 in my buddies gun. Taken from the bottom with action open.
1. It appears that the cartridge guide is not perfectly inline with the bore (it sits to the left of the centreline in the photo).
2. Adding to that issue, the bullet nose skids to the left when it is pushed by the bolt as seen by the skid mark.
3. At the end of the cartridge guide (extreme top in the photo) there is a shiny spot which I think is where an extra rub takes place.
4. The edge of the chamber is shiny indicating rubbing there as well. In some cases when I cycled the ammo (safely of course!) I saw gold coloured material collect on that edge.
5. I took it apart and polished and cleaned up the skid marks on the cartridge guide.
6. I checked the spring tip that holds back the bullet. It had a decent radius as far as I could tell, but I gave it a light grinding anyway. So this was not a real issue for my gun.
7. When reassembling the action, I noted that perhaps the cartridge guide was not seated all the way in (i.e. away from the barrel face). There seems to be more of a gap between the guide and the barrel face now. This would increase the possibility of the nose of the bullet hitting the barrel face as it went in as it was before my teardown. Note to self, always push in cartridge guide till it's stop when reassembling.
8. It appeared that the chamber needed the chamfer treatment. First I tried using 1000 grit paper etc to create this chamfer. However it didn't remove much material. Finally, I put the dreml to it carefully.
I then finished it with 1000 grit sandpaper taped to the dreml bit.
9. The chamber as found:
Here is the final result:
10. A few reference photos:
the dreml bit I used on the chamber. seemed to work ok.
I had to sand the result with 1000 grit emery paper.
A cleaning rod inserted to see the level of misalignment between the cartridge guide and the barrel. It is a bit off, but not that bad. If you compare the very first photo with this one, you will see that the gap between the cartridge guide and the barrel seems to have increased. So the cartridge guide probably was not fully seated initially. (There were no adjustments to the barrel nut)
The face of the action before attaching the barrel. From top down: cartridge guide, the bolt firing pin hole then extractor at the bottom. Note, the bolt is definitely not riding in the center of the cartridge guide, but there is no rubbing.
11. It was time to put it together and run some test cartridges through.
On the left are 3 cartridge from the before mods group.
On the right are 3 more done after the radiusing etc.
You can see the dented tip and scuffing in #2
#3 bullet has a dent in the casing.
And #4 5 and 6 have no dent and almost no scuffing.
I was concerned about the misalignment between the bolt, cartridge guide and barrel, but the saving grace is the bolt, as there is enough left to right slop in its movement that it really doesn't matter when the bolt seats on the chamber.
The chamfered/radiused chamber edge did make a big improvement. So I think I've got it fixed. The next step is some accuracy testing.
