Old topic, annually or semi-annually revisited. Almost all barrels had relieved muzzles. Unlike “coning” today, the rifling extended undiminished to the muzzle in rifles with relieved muzzles. The relief in the couple dozen original barrels I freshed the rifling on was 0.010-0.015”. And no, this was not due to wear or other explanations because that would diminish the rifling, result in ovalization, and so on. This same setup was documented on an Oerter rifle in excellent shape in the Moravian book by Bob Leinemann. Clean, bright, and relieved for over an inch. Now you and I know this is not the way to get best accuracy so some of us close our minds to it like a bank vault. Never happened, because it wouldn’t work for me.
We don’t have to know how they did it, just accept real data. It’s possible that young fellas with great eyesight deepened the grooves by filing, then relieved the lands.
A number of original Hawken rifles were similarly relieved. The result is that a patched ball can be thumbed into the barrel, patch trimmed, and rammed home without any short starter needed. This is what period accounts of Audubon and Boone describe as loading procedure.
The proposition that “they had to pound the balls in somehow” presupposes that the muzzles were finished as they are today. Yes, they did have to pound them in when using late percussion barrels rifled by Remington or others during the established bullet board/short starter era.