From October Guns & Ammo
Magnum Magic?
I may have part of the answer to the question of how the short magnums perform as well as traditional magnums while using less powder. The short magnums come in barrel lengths equal to the long magnums, usually 24 inches. However, this number is from breech to muzzle and does not indicate the length of the barrel in which the bullet accelerates down. As a generalized example, a 7mm Remington Mag. is close to a half-inch longer than a 7mmWSM, because it takes up less room in the breech, has an additional half-inch or so of barrel through which to accelerate. This might translate into an extra 30 or 40 fps. This is on top of any additional efficiency provided by the short, fat powder column. Just a thought.
Marc Smith, Huron, SD
I don't think this is right. A 24 inch barrel is a 24 inch barrel. He seems to think that the case has extra room because it is shorter but all cases set snug inside the chamber.