What makes a "Keith" style bullet is the outside shape, IE: semi-wadcutter design. Most keith bullets for modern firearms do not have a hollow base. I'd say these are late 1800s or early 1900s, when there was still some original black powder guns in use, probably flattened on impact. There seems to be two types of bullets on looking closer, some round nose and a few may have actually had the "Keith" configuration and may be from the late 1940s or 1950s when Elmer Keith was actually involved in developing the bullet style. Incidentally, he first used his flat nose semi-wadcuttr bullets in the .44 Special Revolver that was hopped up to almost .44 Magnum velocities. In the 1950s he collaborated with Smith & Wesson to develope the .44 Magnum Revolver that is still one of the most popular handgun hunting rounds. Monty