My reloading manual shows highest velocities for 44mag just around 1500fps. So you are pushing them hard for sure at 1750+. 44mag was originally designed as a pistol cartridge. Bullets were designed around that application. When 44mag rifles started arriving it just so happened that the pistol bullets worked well in those rifles. Just as an experiment I would take two approaches. Cut back on the velocity, find a load in a manual that will produce 1400-1500 fps with the 240gr bullet. See if that improves groups at all. Lastly I'd look closely at the scope and its mounts. I have old eyes and can shoot 1" groups with my peep sight at 80 yards. And that's good enough for me in a timber gun. You should be able to do better with the scope. Do you have another scope maybe on another rifle that you can swap over and see if that changes things for the better. I would still give Henry customer service a call to see what they advise.