For anyone who's interested...here's the final update on my rifle. I made it to "range" today and shot 25 patched balls. 90% of the hits were within 1" vertically and 1/2" horizontally, @ 50 yds; and 1 1/2" vert and 2 1/2" hor. @ 100 yds. The others were my fault; I yipped. The drop difference b/t 50 and 100 yds was 2". It seems the barrel is OK. NO MORE SHORTCUTS FOR ME!
If you want to know, I shoot a patched ball with 80 gr. of powder and musketcaps for ignition.