I need some help from the experts please. Lookin for info. on a conversion on a Win. 1886. It is marked on the top flat of the bbl. 40-65 and on the first flat to the left it is marked 45/70 Govt. Does anyone know of this type of conversion if so who would have made the conversion, factory??? Any help would be much appreciated.

Best guess is it had a rusted-out bore from shooting black powder, or just not being cleaned, and someone had it bored / re-rifled to the larger caliber to make it useful again.

I think only Winchester could tell you if it was done at the factory, and even they might not know. There are a few companies that do this but since it could have been done years or decades ago .... no telling. You might take off all the stock wood and see if there are any other markings to indicate who did it.

Good luck.

I am a Winchester collector and researcher. I have never seen or heard of Winchester doing a rebore. If a gun was sent back to the factory they would rebarrel it but not rebore. For many years reboring was a economic and popular solution to a bad bore. So many gunsmiths did this over the years I think it would be impossable to find out who the gunsmith was.