Not quite in line with your thread, Roger, but deals with accuracy just the same.
In the 70's I did an experiment with a .50 Bauska 38" twist, choked barrel and unprotected fiberglass rod - sold then as THE Unbreakable Ramrod. It was 3/8" in diameter. I had to recrown quite regularly, every 200 to 225shots as the groups would more than double in size. I mostly shot this rifle at 100yards as it was a bullet rifle, shooting bullets from 370gr. to 450gr., both Lyman moulds. It was very accurate, as long as less than 125 shots have been through it.
After shortening a total of 2", & with the choke almost gone, shortened 1/4" at a time, the original accuracy would not return, I assume due to interior damage from the rod & possibly loss of the choke. I threw the barrel & the fiberglass rod away and put on a round ball barrel and mostly used a hickory rod, thereafter.