Guy at the club has a really nice High Wall in .32-40 that always shot like a champ. A couple weeks ago his accuracy went to Hell and he ran a patch down the bore. It came out looking like he'd run it across a machine shop floor, only the splinters were lead. They were long, maybe 1/2" and surrounded the patch. So, he cleaned the barrel and fired a couple more rounds. Pushed another patch thru and damn if it did not look as bad. From the amount on the patch, it looked like 1/4 of the bullet was staying in the barrel.
He went home and tested the hardness of his bullet. They were rock hard. It appears that the mix in his lead pot got away from him. Probably dumped in something with antimony and thought it was pure lead. Free lead can be a double-edged sword.
He cast up some new bullets and the accuracy returned.