Randell -
The question has arrisen about smooth bore accuracy, i.e., is there anything more accurate than patched or saboted round ball, as you've suggested the miniball.
Since I lob chunks of concrete filled cylindrical containers high into the air (where wind has great affect) I am satisfied with otherwise to be considered mediocre accuracy.
BUT, the folks that are in COMPETITION are the ones that become experts at the game.
This leads to the issues that affect accuracy (in particular in smoothbores).
Of course accuracy is greatly improved by reducing the time of flight (less time for the wind to have effect) and by spin stabilization (via rifling).
So without spin stabilization what does work is forming the bullet with a large hollow base. It doesn't make too much difference (accuracy) by sealing better, but the heavy end does fly better (example: shotgun slugs).
I did see the winnning target one year from the team that won the cannon competition from the N-SSA (the team was from Petersburg). If I remember right it was a 2-1/2" diameter slug that was about 2-1/2 or 3" long and mostly hollow. (The skirt was 1/4" or so thick.) The target (100 or 200 yards?) had BIG ROUND holes in it - indicating stable flight.
(Right after seeing this - 15minutes or so - the hurricane came through and did serious damage to Petersburg. 45 minutes later on TV we saw the spot where we parked filled up with 4' of bricks - THANKS LORD!!!)
So, to build a two piece mould to cast a skirted wadcutter is no great trick. MEASURE your bore, subtract the clearance you wish to use - .020 .030 .040 or .050 or thereabouts. That's the diameter of the finished bullet. Then calculate the shrinkage for the diameter (dependant on the alloy) and that will determine the ID of the mould.
