.450 - the Lyman Shotshell Handbook, 3rd edition, has some good data in the rear for all the gauges using buck, ball, Brenneke and slug data.
; Because this is an older edition, the powders used don't include Longshot or other more modern powders, however the data is rather exciting to say the least.
; The wad columns noted in the data, closely approximate what I found to work well in my double, so many years ago.
; Data for a .690" ball, (both Lyman and Lee make this mould) as well as the Lyman 475gr. slug, some conical 12 bore slug I don't know about as well as Brenneke slugs shows data from the mid 1,300fps range to almost 1,600fps.
: Powders used are Blue Dot, Unique, Herco, SR 7625, SR 4756 and Hi-Scor 800X.
: The loads running mid 1,500fps are duplicates for the African 12 bore BP load of 7 drams (190gr.), yet recoil is down in the 2-3/4" mag. shotshell range. Various shotshells are used.
: I hope this isn't a duplicate post.
: I've just loaded up a bunch of test loads using 35.5gr. 4756, 3, 1/8" cards and the base of a steel-shot wad for keeping the slightly undersize .722" WW ball I have, in the centre of the cylinder bore. Due to having the cards on top of the powder, instead of a sealing plastic cup wad, more powder is needed to achieve roughly 8 to 10,000LUP. I suspect I'll have to get up around 40gr. to get the requisite velocity in the 1,550fps range from my old pump-gun. In my load, the plastic wad is directly underneath the ball, and allows a standard fold crimp in the target hulls I have, yet shows the ball in the centre, for easy identification.
; I do like your gun.