4756 and 7625 are also useable as these are what I used in my RB 12 bore loads. Unfortunetly, burn rate is only one of the factors in comparing powders. Energy per grain is also high on the list of determining factors.
; With round ball, one could start around 24g.r of either 7625 or 4756. 7625 is the faster of the two, and may give better results with round ball. I seem to remember that 4756 was used in and around 30 gr. charges with round balls and enough wads to fill the case. I used the cupped base wads, base cut off and cup-up to hold the undersized ball in the centre of the bore. One was used cup down on the powder, then filler wads, then cup-up to hold the ball centred. This was necessary for accuracy in my smoothbore.