I picked this up years ago--decades actually--at a Minnesota Arms Collectors Association Show held in (of course) an indoor ice arena.
It was sold to me as a .32 mould and I wanted to try it with a .32-40 I had acquired, but darned if it doesn't cast .340. It's a good quality piece, and I've often wondered who made it, but never found out. It seems to have a lot of Hensley & Gibb-style features--in particular the little windows showing the ends of the mounting screws--but it's not H&G marked. The only markings are "A-340-750" over "1 0 2 5" on one side and two "1"s (one on each half) which I assume are assembly numbers.
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If you happen to know what it is/who made it, that would be great.
Now I'll step aside and let the experts chime in.
--DJ