What gun maker mark has two crossed swords handles up with a three point crown between handles?
Not sure without seeing the mark - but it sounds as if you might
be describing a proof mark, rather than a maker's mark. The
standard proof mark for black powder shotguns made in Britain and
proofed at Birmingham featured crossed somethings (I'm not sure
they're swords, but they look something like swords) with a crown
at the top between the ends. As a standard shotgun proof mark it
should have the letters B P C between the crossed items, in the
gaps other than the one with the crown. This mark also appears just
with a V opposite the crown, as a view mark, indicating the gun was
inspected at the Birmingham proof house.