Well, I shot the conicals. Used my .40 Green River 36" barreled percussion Hawken I made. Shot 70 grains of Goex 3F, .40 Lee mold conical, weighed about 183 grains, miked about .403. They were lubed with some kind of reddish lube. Had to hammer the short starter to get them into the barrel, then drive them down with my steel range rod. Three shots was enough. Averaged 1644 fps, at least a 4" group. (One missed the paper).
For comparison I then shot six .400 cast balls from Track of the Wolf, with .012 pink and white pillow ticking and 60/40 Murphy Oil Soap and alcohol, CCI 11 caps, and 70 grains of Goex 3F. They averaged 2010 fps with 82 spread, first shot out of the group, then 5 in 1.5" at 50 yards.
Everything the same BUT .395 swaged Hornady balls, five went 2101 fps with 47 spread, 1.9" group, three in one hole.
Then I shot a Muzzleloader Builder Supply .40 flintlock "after the manner of Christian Beck", 36" Green Mountain barrel, I built. Same load as above, that is, .400 cast ball and 70 grains of Goex 3F, six shots went 1929 fps with 84 spread, 3.1" group.
Then I shot the .403 conicals in it, with 70 grains of Goex 3F, smearing SPG lube onto the bullets. Six went 1531 fps with 72 spread. They loaded pretty easy (the Green River barrel is tighter). First three shots in 2.5", next three off the paper.
I know little about shooting lubed cast bullets, but have found out that this bullet requires more work to shoot well. Perhaps it could be sized to .401, but that is beyond me now. I like the idea above of using a .380 with a patch, as mentioned above. Would like to try that.