No idea. I got it off an auction site a few months ago. Figured i"d learn how they were put together before I fired it. Tore it down according to a book and found a small crack on either side of the sleeve about midway on it. The buffer was missing on the rod the inertia piece travels on too. Perhaps this was the cause. Do you know if replacements are available?
Jethro: I don't think the buffer missing would have caused it. Could you see any damage to the receiver raceway for the sleeve?
I think you would be better off replacing the bolt sleeve rather than welding on yours. Brownells carries the parts you'll need.
First stop: Browning Customer Service. Then decide what to do with it. Many parts are available only as a factory-installed part, I would guess that a piece of the fire control would fall under that, but it may be an OTC part.