The problem with buckshot is that each individual pellet is a poorly performing projectile, both externally and terminally.
A one ounce load of buckshot will not penetrate nearly as well as a 435 grain .458 LBT at the same velocity, especially so if heavy bone is encountered. Nor will the buckshot retain it's velocity as well, and as range increases, so does the distance between each individual projectile.
If I used a shotgun, I would prefer a saboted type slug. And I seriously doubt even they would have the penetration of a .45-70 and a 435 grain LBT at 1750 to 1800 fps. Or a 540 at 1550.
