How about this for a scenrio:

A professional pattern maker who happens to like tinkering with guns, makes a high quality mould/ sand casting for the manufacture of some aluminium forends for No1 Mk111's. He skillfully knocks out a few thinking he might be able to sell them or use them for target shooting or that they's be ideal for hunting deer in the highly temperature variable wilds of Canadaicon, and he just happened to have some Ross buts lying around or maybe he preferred them for some reason and put them to use.

I don't know anything about them, but skilled people can make excellent products that would appear to have come from a "line". Especially moulded products.

Just my 2 cent and nothing more.