Theres 4 tubes on blocks at the Civil War Memorial in Natick town square. I will check them out this weekend for round or sharp shoulders. As l recall one gun was from each of the 4 MA foundries that had Govenment contracts; Alger, Ames, Hooper and Revere Copper.Most guns and plans have the rounded shoulder at the breech as seen above, but Napoleons will be sometimes be seen with the sharper shoulder, as shown in the lower portion of this illustration. Depended on the foundry I suppose.
I need to dig into this more . . .
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PS: My Napoleon has the sharp shoulder.