HH: I've pondered those questions myself for a long time. Studying Gordon's vol. III which contains dozens of examples of Hawken and other plains rifles, there are none that have a crown as we know it today. Now you and I know it would be impossible to load a barrel that is cut off sharp at the muzzle. So what did they do?
It is my opinion (guess) that the muzzles were filed. The grooves and the lands may have been filed with a taper as they exit the bore, leaving the edge sharp but allowing a patched ball to be seated, possibly with the thumb, flush with the muzzle. You see this a lot in European arms, in Steinschloss Jaegerbuschsen, for example, where the rifling is exaggerated by file work in place of a cut crown. I cut the crown on my Chambers Virginia rifle this way, and I like it.
On most other rifles, I cut my crowns, usually in the lathe, at about a 60 deg. angle, but then I polish with abrasive cloth and round all edges, so there is no angle at all. This allows a very tight patch/ball combo without risk of cutting or tearing the patch.