Agreed on all points. Our unit used a home-made cannon that we, being teenagers, probably trusted too much. However, the college boys in charge of our reenactment unit always stressed the points you made, and woe be unto anyone who neglected to dip and swab the tube between shots.
We never fired anything solid. Everyone in that group of enthusiastic 'yutes' (as My Cousin Vinnie would say), understood that would have been asking for serious trouble.