Like Dan, I already have a bore calibre rifle for large game. Mine is a cap-lock single shot .69 cal. = tight 14 bore in which I use a .684" pure lead ball or 15 bore .677", WW ball. I tried the larger .684" mould (similar to Lyman in design) in WW but unless in paper ctgs. they cannot be loaded as a thick patch is required to seal the .012" rifling, for accuracy and clean shooting.
The rifling is .012" deep and the rate of twist is 66".

This rifle is exceptionally accurate MOA at 100yards and holds that accuracy all the way from 140gr. 2f all the way up to 200gr. of 2F, delivering 1,700fps with that charge. My best 200yard group off a hand rest on a bag while sitting at a table, was a rectangle 1 1/4" wide X 3 1/2" tall for 6 shots. There was no wind.

The recoil of heavier charges as in 180 to 200gr. charges was WAY to much for me so I settled on 1,500fps with 165gr.2F as being usable and that's my moose load. It staggers them with mere centre rib hits. Such a hit with a WW ball will make a 3" round hole though both lungs on a moose. They then dump all their blood, almost instantly. Death is very fast. I'm sure the slightly smaller 16 bore ball will do just as well and will kick somewhat less, having a lighter ball and slightly ligther charge for even flatter shooting.

My concern about modern Forsyth-type barrles is that if the twist is made too slow, the charge required to get good accuracy might be too high for me and many others to shoot. I'm getting too old (old injuries haunt me) for the heavy thumpers.

I'd like a 16 bore barrel, 80" twist and shallow rifling is good, (I would like .006" or .007") to replace my 14 bore barrel right off the bat. I'd like to hold the rifle's weight at 9 1/2 pounds or a bit more, so 1 1/8" tapered to 1" over 32" would be about perfect - octagonal, of course, or round octagonal with wedding bands. That way, the 'old' underrib and breech will fit perfectly.

My 15 bore mould for WW balls is a Tanner, without a sprue cutter. I use the plyers-type wire stripper with little cuttouts to cut and then twist off the sprues that are attached to each ball. Every now and then, a quick swipe of a rasp is needed to fully round the ball. Generally they are perect as snipped/twisted. I tried using side cutters, but prefer the wire strippers by a long shot.

What I really appreciate about the tanner mould cast balls, is the absense of a sprue so orientation of the ball is not necessary.