i will be the first to tell you i dont know about double rounds all my info is from here or the few books that carry it.or the info from the net and this forum.so i ask is hornadays ammo to hot for this double.400 i just am a novice all i saw was the numbers and i still dont know what they mean i know saami is used here and cip is international but that is all i can tell you about the two.