According to SAAMI, all large rifle (to include magnum) cartridges are to be shot with 24” barrels when testing for data and pressure. However, because of the large case capacity of Nosler and Weatherby cartridges, they see magnificent gains in velocity with longer, 26” barrels. The extra 2” of barrel allows for the slower burning powders typically used in magnum cartridges to completely burn thus achieving higher velocity.