Thanks Tim for the information.

Regarding the proof marks. By 1876, should there not have been more marks than the crossed sceptres and the number 13 that I described in my above post? There is no fancy intersecting BP below a crown or a muzzle diameter number or a not for ball etc. which indicated to me it is from 1855 or before. Or did black powder muzzleloaders not require all the proofs that a breech loader would?