Bill - thanks for the barrel makers address. I find great pleasure in sharing what has worked for me, hoping this experimentation will advance other's enjoyment in the sport.
: Tinker-- it is possible you are getting in the relm of 1,100fps to 1,200fps due to no gas leakage at the breech, being a ctg. gun compared to a muzzleloading rifle. 2 1/2 drams is pretty light to expect more. I will be interested in hearing your actual chronographed results. With double guns, the thickness of the barrels towards the breech, adds considerably to the elevation given the ball. The thicker the barrels, the higher the elevation given. Of course, you are compelled to use a load that will regulate the barrels as well. It is possible, Swiss powder will be the best for that. In intermediate target will show actual elevation. By that, I mean, have a load zero'd at 100yds. Then with that sight picture, shoot at 50 yds and note the elevation given the ball. The higher the sights are above the barrel, the shorter the actual point blank range, and more powder merely gives greater elevation, without extending the point blank range. With low sights, more powder merely makes the ball fly further, without adding more than 1/2" or so to the elevation.
: The lock on my smokepole is a good one, with a buggy spring-type main spring. The cap is opened at the front when fired, but remains on the nipple until the cock is pulled back. There is very little escapement tof gas, but some, of course, or the cap wouldn't be opened up at the front edge.
: This statement pertains mostly to muzzleloading rifles. It is a wonderful thing, to have 100yd or further point blank range with a large bore rifle. The ball, in it's trajectory, travelling no more than 1 1/2" above, nor below the line of sight to that range. Low sights and a 14 or 16 bore rifle will deliver this, if sighted properly, and having the proper depth and twist of rifling.
: Fellows I shoot with, & have tried my .684 RB's in their 12 bore choked guns, and have loaded thin cloth patched round balls in their shotshell cases. This may work with yours as well, Tinker, if the ball is slighty undersize to the groove. Even from a smoothbore duck gun, they were getting 5" accuracy at 50 yds. rest shooting, elbows on the truck hood and single bead front sight.(with smokeless powder)
: I have used the cup base from retrieved trap wads(at the range). When the top piece is cut off it leaves a cup of plastic with flat base. I seated 1 or more as needed card wads on the black powder charge, then a plastic cup on the wads, cup upwards, The cup held the ball in the middle, and I merely crimped the hull over the ball. This load system shot about the same as their patched balls, but of course, if patched balls with LeHigh Valley lube or some other BP lube, keeps the barrel's fouling soft and easily removed. My 12 bore BP loads without a cleaning patch, left the fouling hard and caking. The cloth patch on a slightly undersized ball turned out to be a good move in regards to clean shooting. It might be worth a try.