Uhmmm, isn't the MAIN reason for the .460 for safety & liability reasons - i.e. the longer case prevents the gun from going into battery if you try to shoot the round in a .45 acp gun. Unlike the .45 super, where dopes can shoot it (and thus kb it) in .45 acp guns? This also answers your question about headspacing, IINM. The bbl chamber must be reamed to that fractionally longer dimension, or the gun won't go into battery. If the longer case IS indeed "within specs", then it would go into battery, which would negate this main safety reason for the round, no? So, same mags, but different bbl, I believe. This results in less peeps blowing up their guns and suing the makers of the cartridge, as undoubtedly will happen with Triton, etc. The weird 460 name also I believe contributes to the a lower liklihood of peeps suing 460 rowland ammo makers, because it's SO different from ".45 acp", requiring greater negligence to chamber in a gun stamped ".45 acp", unlike ".45 super" - ".460" adds an extra digit (the zero), and adds a different second digit - six instead of 5, thus giving the ammo maker's attys much to make hay with WHEN they get sued. Liability, liability, liability!
Oh yeah, and slighty more ballistics, too.
PS. We could argue whether rowland or super gun's barrels actually have stronger bbls and more fully supported chambers, but it gives ammo makers somewhere else to cast the blame when they get sued for a kb, besides allegedly weak brass or overloaded charge relative to brass strength (or deep seated bullet or whatever). If peeps shoot rowland in acp guns, it's much easier to cast the blame on "wrong gun" than for example Triton - certainly they can and will (after all, their round is NOW the .450 xxx - forget the name - that's prolly why they called their .45 super this now, come to think of it!). If someone sells something called ".45 super", then it's a little easier for dopes with metal shavings embedded in their face to sue them when they shoot it in their old "forty-fahv".