It' s an old designation that is still used today. When metallic cartridges came out, it was common to see this type of designation on cartridges. The .45-70 means 45 caliber/70 grains of black powder. The Contender can also shoot just about any rifle cartridge.

The Ruger Redhawk is a fine revolver. So is the Taurus Raging Bull. The .454 is probably the .454 Casull. A true flame throwing, monster killing cartridge, with recoil to match. The above guns in that caliber are usually ported to tame some of that.