Doesn't the soft ball obturate a little to help fill the grooves?
Not likely at all in the smaller sizes & especially with loose combinations & small balls. I think the .574's were obturating in my Musketoon, as the rifling was
.008" deeper at the breech than at the muzzle, yet patches were reusable. A .020" patch with .495's in my .50 were not quite sealing, as brown scorch stripes
are witnessed on the recovered patches, running from the bearing ring out to the outside of the patch. These still shoot cleanly enough that no wiping or SWABBING
is necessary while shooting.
Many people who use thin patches cannot find them on the ground after they are shot, due to just burning up into blackened threads & pieces of charred cloth.
My .595's in the 20 bore also oburate as there is a slight choke, yet those patches are also reusable.
All patches fray around the edge and that is due to muzzle blast. The weaker the material, the more fraying there is.
This is a 5-shot group from a rest (portable table rest) at 25 yards. Shooting at this range, does not prove a load and is only done as a test of aiming precision.
Through this type of testing I have found that the undersized 16 bore ball, when fired with a sealing patch of .034", shoots 3/4" to the right of my sights + an inch high,
set for the full sized ball of .682" when used with a 10 ounce .021" patch. It pays to shoot on target when changing any components.
This "group" is 7/10" centre to centre from my .69cal. rifle.