Interesting mold. Maybe someone knows something about it. Haven't cast with it yet so cant give you the diameter specs and the throw weight although its listed at 488 grains at the Three Peaks website.... The Lyman Handbook of Cast Bullets lists it as "You name it, we've got it (.454 first band, .465 2nd band, .447 two rear bands.) The base looks quite similar to the Lyman 557489 which is the Sharps Carbine boolit where the powder charge bag is tied onto the base of the boolit.

Could this be for a .45 caliber breechloading rifle? Whitworth perhaps? I'm sorta stumped.