The one and only time I shot prone with a muzzle loading rifle was in a cartridge rifle match in 1976. Ten shots - five at 100 and five at 200 yards. I used a round log section for a rest. In those days I could see. I used my .62 cal Hawken rifle and won the match, much to the chagrin of the cartridge rifle guys. First prize was a Dixon's leather covered powder flask, which I still have and use. I was shooting 120 gr. of FFg at that time, and cannot say that it was particularly uncomfortable. I doubt I'd try it today though.