I use the base gas check cup, cut off a plastic shot wad, one down on the powder, then whatever fibre wad needed for height, then one gas cup, cup-up underneath the ball. The cup centres the ball in the bore, no matter what the choke.
: Since there is no loading data for 16 bores for ball that I know of, you have to measure the tightest bore you are going to use, and use a ball that size or a bit smaller.
: A full 40 points of choke in a .16 bore, would have a .622" hole at the muzzle. This means a .622", .620", .615" or .610" ball would work. I tend toward the heaviest ball I can use in the smaller gauges, so would order a mould from Jeff Tanner in the UK at the exact size I wanted - in the above cae, a .622". I would use WheelWeights for my alloy. At .622", the ball does not need expansion and penetration will be wonderful.
; As to loads, since the ball weighs only around 340gr. or less (down to 310gr.depending on size), this is only just over 3/4oz. so any shot load with that weight would be the place to start with loads. Use the slowest powders you can, as they will give the highest velocities. Round balls develop less breech pressure than does a load of shot, even though of equal weight, so some slight increase is allowed. You should easily be able to breech 1,400fps with a round ball. If loading your own shotshells is all new to you, only use the loads given an a shotshell manual.
: If you want more power than that, you can use black powder and as much as you can get into the case, still leaving room for 1 or 2 card wads on the powder and the plastic cup gas check wad underneath the ball. You can use either roll or folded crimp. I used a partial fold on my BP loads so they're recognizable and full crimps on my smokeless loads. A Lee hand die set for 16 bore is all that's needed. The wad guide, decapper, recapper and cromp starter are the important parts.
; BTW- shooting BP is fun. Just don't put plastic directly on black powder. The heat of the BP burning will melt plastic onto the bore - you don't wand that.
; Good luck and keep us posted on your results. As with any sort of loading, one must be open to having to juggle loads to improve results. This type of handliading is not different that working up a load for a rifle, handgun or shotgun. You cannot merely pick a load and have it be the best - it might be, or you may have to work up the load as I did - in just about every gun I ever loaded for. Different powders, different wads, even different primers. You must have a powder measure, beam or electronic.