I was thinking about this and had an idea. My theory is that the middle of the groove is to deep to get patch compression.
An old Lyman black power book showed a picture of the ball with patch impressions on the lands and grooves and being a "correct" combination.
We now have CO2 dischargers. Has anyone tried loading different combinations and using the discharger to eject the ball and patch in to a rag cushion and then examine the ball for sufficient patch compression?
My latest flintlock pistol build was really hard to start a .440 ball . I had cut the muzzle of the barrel. and had it quite square. When I made my crown I tried to emulated what was on the original muzzle. I was using JO Anns cotton drill #40 with bear lube.
When I shot it the patches were awful.
When I went back to my shop after cleaning it, I loaded without powder. I marked the ramrod to seat the ball 1/2 inch above the breech. Got may discharger and clamped the barrel in my vise, and let it rip into a cardbox with some Wall Mart bags inside. I found that the patching was cut at the edges of the lands.
I got a 5/8 inch stone burr and went at it with slow speed with my drill. Did a little bit and reshot it . Checked the patching and it was better. Repeated this till there was no cutting of the patches. Then I smoothed it out with the patented Daryl Thumb method down to 320 grit.
Placed barrel back in pistol. Placed on my loading stand and reloaded it again without powder. The ball loaded much easier ad I shot it into he box and the patch looked great.
Verified the experiment at the range with powder . The patches looked great and the accuracy ws also great. Saved me a lot of time.
I would do it again on a rifle if I have the need.