Thanks for all the advises.
I shoot again yesterday.
Rise the charge (using REAL 440gn) from 80 to 100 gn (vol) but loose accuracy so I tried 90 gn (vol.)

From the bench I can not get consistent groups. I use a collapsible working bench and sit low so my back is vertical.
Eight shots forming two good groups:
Group A: R1, L1, R3, L3 into 3”, almost round but low (3”) and to the right (2”) of the aiming point.
Group B: R2, L2, R4, L4, into 5.5” left on left side and right on right side but high ( 3”) to the left (2”) of aiming point.
I think that this two groups are because the way I hold the rifle over the bench but I can also have problems with the loading system (muzzleloading rifle).
Then I shoot standing resting my front arm on my truck and get a bigger group 5 Ľ”, low (1.5”) and 5” to the right of aiming point.

As I’m alone when shooting I shoot to two targets side by side, right barrel to the target on the right and left to the other. Then I copy one target over the other to get composite group.

Thanks Martin