Are you allowed to wedge the wheels? .Try placing a wooden wedge snug behind the left rear wheel, to retard the recoil impulse. See where your POI goes from there.
Another technique I use on my Dahlgren is to shorten the breaching ropes on left side to move impact to the right. I am not use to the degree of precision you are dealing with, but maybe it could help.
Another technique I use on my Dahlgren is to shorten the breaching ropes on left side to move impact to the right. I am not use to the degree of precision you are dealing with, but maybe it could help.