Let’s review on what you have learned so far:

70 gr powder doesn’t work for this gun.

90 works much better but you still don’t know if that is this guns sweet spot. You need to experiment some more

center the ball in the patch (not sure that was a major problem)

clean between each shot. I use a wet patch followed by a dry patch

changing amount of powder changes your POI (point of impact). Any time you change the amount, you will have to adjust the sights.

Always experiment at 25-30 yds. Don’t move back until you have the best accuracy you can get, then change your sights for longer distances.