Of course they can be shot! Might require re-barreling or installing a liner. Many Martini-Henry rifles have no safety. Which is fine, just don't load them until you are ready to shoot. They are black powder actions. So cartridge selection would be like 50-70 or 45-70(with light or black powder loads) or other black powder cartridges. Most are found in old, odd European calibers(so re-barrel).
Just walking on the edge of of my grave.