My findings as well at the chronograph, DP - 3F giving higher shot to shot velocity swings than 2F. Over the years, I've found 2f to be more consistently accurate than 3F as well. It fouls more in the vent area of the flinter, but this is easily addressed by pricking the vent now and then. In a cap gun, I notice nothing other than improved accuracy AND less demand for an extremely tight ball/patch combination - due to the lower/slower pressures of 2F.
In the .58 and .69, my shot to show velocity spreads fell to below 10fps on 10 shot strings with select accuracy loads when using spit for lube. Using grease/oil for lube, ie: bear grease or mink oil would double the shot to shot variations. I also noted that the heavier loads in both .58 and .69 gave the mallest variations shot to shot in velocity spreads. The light loads generally gave the largest spreads - same ball and patch.
Wiping between shotsalso increased the shot to shot spreads, while shooting 'dirty' reduced shot to shot spreads. That indicates a more consistant bore without wiping. At 50 yards, the first shot is usually an inch out of the group, but is fairly consistently placed - no problem while hunting large game.