hepburn 40/2.5

[bruce moulds]

a friend recently acquired an original hepburn 40/70 straight.a chamber cast reveals some interesting things, although it is only an assumption that the chamber is still original.
base diameter is 0.462, which seems a little larger than expected, but not overly so. bore and groove diameter have yet to be established, due to an odd number of lands and grooves.
rim thickness seems to be about 0.070, again a little thicker than expected.
the chamber has what appears to be between 7 and 4 degrees transition which is also the leade angle.
neck diameter is 0.426 at the front, and has no parralell section, the case being tapered right to the front.
assuming cases with 0.010 thick necks, this would allow finger seating of a bullet 0.406 in unsized cases.
this would suggest a pp chamber, to be used with sized cases and possibly tapered bullets, or a bigger bore than 0.400, or a chamber modified but still too small for groove diameter bullets.
I will patch some bullets to different diameters, and use them like pin gauges using a breech seater to establish a correct bullet diameter.
a most interesting project for a lucky guy.
keep safe,
bruce.