Much like Dimmick rifle bullets, these will be found in almost any diameter for their specific rifle. The diameter of the round itself will be smaller than the bore of its weapon because they are designed for muzzle loading tige rifles. These rifles employed a strong "pillar" at the breech upon which the solid bullet was rammed/hammered to cause expansion into the grooves. Expansion prior to firing as opposed to the minnie ball principle of expanding during firing. Cool bullet, possibly from Mexican service?