Created in 1973 to commemorate the 100th anniversary of the adoption of the .45-70 cartridge by the US military, the Model 100 revolver is a behemoth of a six-shooter. It was made by Earl Keller and Gene Phelps of Indiana, under the name Century Mfg, Inc (no relation to Century International Arms). The design is a Single Action Army Colt scaled up, and was made with a bronze frame, and with a cross bolt safety added. They were initially chambered for .45-70, but this expanded to include .50-70 (“The Mother Load”), .375 Winchester .444 Marlin, and .30-30 Winchester.

Phelps and Keller parted ways in 1976, with Keller continuing to make the guns the same way and Phelps changing to stainless steel and abandoning the cross bolt safety. In total, something close to 3,000 guns were made in total between the two.