The cannelure is to prevent bullet setback, and most if not all, the early production ammo had that feature. The three dents acted as a positive lock to keep the bullet in place. They tried a lot of things in those early days to make sure the ammo worked as it should. By the end of WWII, they found that neck tension when used with the black asphaltum cement was sufficient, and the cannelure had mostly disappeared.is this as old as 1918, or when? Next to more recent cartridge.
The crimp looks like a seating depth ring and there are three of the small dot-dents spaced equally that appear to hold the bullet in place.