I gave this thread some more thought - but I was stopped before any damage could be done - and a couple of things deserve mentioning-again. 100 grains of powder in a 20 ga is way more than needed; too much actually. My smoothbore has a rear sight and I don't think I would have kept it otherwise. It helps with both ball and shot.
Stock shape can make a major difference, but getting the face up a bit does the same thing. I shoot ball, prb and bare, with 60 grains of 3F going up to 70-75 for deer. But as I no longer hunt, 60 grains it is. The 20 ga isn't much of a kicker so that alone tells you something is not right.