Dave, Hodgdon's 2004 manual contains a Pyrodex recipe for a one-ounce 16 ga 2.75" load, as follows: unspecified hull and primer, 90 gr. Pyrodex, card & filler. 1128 fps, 5600 LUP. So, I'm thinking 75 gr. will be too slow for effective shooting with shot smaller than #5.
Hodgdon also advise against the use of powder measures designed for smokeless powders.
Brent, Hodgdon recommends 80 gr. Pyrodex, card & filler, and 1.25 oz of shot. Yields 1040 fps, 6000 LUP. Tom Roster says 1050 fps is plenty for #5 shot. Bottom line, I think your load should work well.
I don't know where to find actual BP data, especially any using the BP available today. Even then, brands differ significantly in power. If I were doing this, I would load up a few rounds and use the old Dixie Gun Works tin can penetration test. DGW figured if you could penetrate a tin can, you had enough velocity to go hunting.
Sam Fadala has a BP loading book out, generally available in book stores like Barnes & Noble. Might be worth a read.
