Hi Bug:
I just received a new 10" .357 bull barrel from Ed that has this same type of bolt. First one I've seen, and it seems a lot looser in the barrel lug than the older style. The profile of the top of the bolt parts is different, too; more stepped rather than tapered. I haven't tried it on a frame yet, so I don't know how it will work or lock up. Maybe I'll get around to it tonight - so many guns to play with, so little time!
RonF