You will need a "Taller" front sight..not a lower one to bring your POI down.

Generally speaking, the heavier the bullet and the slower it is moving will result in a Higher POI. Because of inertia and a longer "dwell time" in the barrel...giving the barrel more time to rise before the bullet exits.

HSM "Bear Loads" are not that hot..they are actually designed to be powerful, yet "controllable"...With that being said, they are classified as +P because SAAMI spec is very low in the 45-70 to accommodate the 1873 Trapdoor.

So you may find that the HSM actually hit lower than the slow Remington, which is loaded to Trapdoor pressures.