How big is a 25x59mm caliber?

The 25x59 calibre round is a grenade that has been adapted to be fired out of the XM109 Anti-material rifle, the XM25 Individual Air-Burst Weapon System as well as the XM307 Advanced Crew Served Weapon. The cartridge itself is just over half the size of the .50 BMG Heavy Machine Gun Cartridge, whilst the diameter of the round is just under twice the width. Examples of the round can be found in this handy diagram; http://www.globalsecurity.org/military/systems/munitions/images/xm307-25mm.gif