Problem with a MkIIIB bolt jumping its track

I just got a pretty nice MkIIIB Ross, but the bolt is giving me some trouble and I wonder if anyone else has experience with the problem. When fully opened, the bolt head often (about 50% of the time) jumps off its guide rails and starts to rotate. I can usually get it back down and horizontal, and when I can it will close just fine. But the rear sight bridge interferes with getting to the bolt head in this position, and sometimes it rotates significantly and gets thoroughly jammed up. Once I managed (unintentionally) to get the bolt head fully rotated into the locked position with the bolt in the fully open position. I disassembled the rear end of the bolt to remove spring tension on the bolt head in order to unjam the bolt.

Is this a problem with a well known cause and/or solution? FWIW, the bolt has not been safety riveted (although I don't expect that would have any bearing on this issue).

Attachment 44699

I have not heard of this one before, and not being the Guru of all things Ross I tried to duplicate your problem with my MkIII. I do not see your rifles ejector in your picture so I disassembled my rifle and removed the ejector. My bolt won't rotate out of it's ways with the ejector removed as the bottom edge on the left side keeps it in place. If your ejector were indeed missing it's installation may help alleviate the problem as it appears that it would help prevent the bolt head from rotating too far. I lightly wedged my bolt head to try to approximate yours but the bolt head cannot get past the same edge on the left side. If you compare my picture of the left edge that my bolt head cannot clear (just above the ejector slot 1st pic)) and yours where it can, you can see that yours has a bevel and mine comes to a sharp edge which may give mine less clearance to rotate. Perhaps someone else has seen this before and can offer more insight. Regards. Tom

Never heard of such a thing myself and I can't see how it would occur. Are you sure someone has not ground the locking lugs down on that side, perhaps to conceal damage or remove a chipped area? You might have one of the over-hardened bolt heads from Col. Harkom's attempt at heat treating in France.

Some photos with the bridge removed would help.

The first thing that rifle needs is a damn good cleaning.

The locking lugs look fine (and the rifle does have its ejector; it was just compressed all the way in that photo). I took the rear sight bridge off, and it looks like the left side guide rail behind the ejector is a bit boogered up. I think that's allowing the bolt to rotate slightly just as it passes the ejector.

Attachment 44779Attachment 44781Attachment 44782Attachment 44780

FWIW, once the bolt starts to rotate and jam up, it seems that it's only the ejector preventing it from rotating completely. If I push the ejector in with a finger, the bolt immediately snaps almost fully into its locked position:

Attachment 44783

The break in the guide rail is visible here above the ejector. How such a piece would get broken off I do not know! Perhaps fired with an unlocked bolt?

https://www.milsurps.com/attachment....1&d=1374763123

You've figured it out by now of course, but just posting this for possible future reference by others.