RHB - round balls are fine in choked barrels as long as the ball is the same size or smaller in diameter than the choke's smallest diamter - which is usually .690" for full choke in a 12bore. My buddies worked up round ball loads for their full choked duck 12 bore pump guns for use on moose while duck hunting. If using cloth patches as they did, one would need to use a ball smaller than the bore, to make room for the patch. They used a .684" ball and very thin linen patch.
; If lino or any really hard lead is obtainable, you should cut it with pure lead about 1/2 and 1/2. Lino and babbit lead is brittle and will shatter on impact with hard bone although maybe not at low velocities of a shotgun - I don't know for sure, haven't tested that.
; Black power makes re-loading shotshells dirt easy as long as one can get primers and wads. Never let plastic wads come in contact with black powder. When fired, the flame fornt will melt plastic onto the bores. always put hard cards between them.
; A simple Lee wad starter is all that's really necessary to get a cone shaped crimp over the ball when using plastic cases. A lee loader hand tool set is even better. You just use wads to fill the space between the ball and the powder, along with the plastic gas check with the cup holding the ball in the centre. My buddies used cloth patches around the balls instead of the gas checks. They were good for about 5" at 50 yards. Plastic gas checks are cut from spent trap wads at the local club - free for picking them up. Many different types can be tried, many will shoot slightly differently so allow experimentation themselves.
; I'd not shoot anything less than about 4 drams black powder, and actually had my best results using black powder with 5 1/2 dram (150gr.) loads in my double 12. It will kick in a light gun.
; In the past, round balls received bad press and the 'memory' of their dismal accuracy still accompanies them today. They were developed in the States back in the 1920's for shotguns and typically used naked round balls .630" to .640 in diameter that bounced up the bore and shot all over the globe. In other words, they were too small for a 16 bore, yet were loaded in a 12 bore case. It is little wonder round 'Pumpkin' balls obtained a poor reputation here.
; Making the balls larger and giving them proper steerage up the bore (cupped wad underneth them) lets them shoot as accurately as any smoothbore can shoot. One can jungle the load somewhat to make them shoot even better - diferent charges, different wd columns, different lubes? Lots of 'work' ahead of you. As with anything worth doing, there is experimentation to do. Lee makes a .690" ball mould for around $16.95 US and Lyman makes the .690" ball mould for about $75.00 US. Lee is aluminum, Lyman is iron. Jeff Tanner in the UK will make any size you want for around $30.00 from brass, shipped to you in about 7 days - you will need handles for the Tanner moulds and Lyman. Lee comes with handles. I have two of Tanner's moulds and they are superb for the money - a .725" and a .745".