Same ballistics as each other.

Which case head are you talking about, the 500/416 or the 416Rimmed Rigby? If the Rigby then it is the same head size as a 416Rigby if the 500/416 I do not know. Have to look it up.

Good on Rigby for developing the new cartridge. Though I note the 416 Rimed developed by A Square in the early 90's is a blown out and lengthen 416 Rigby case designed specifically for double rifles. I do not think you can find these any more. I hope the new Rigby cartridge succeeds where the A Square did not.