Introduced in 1958, Winchester introduced the 264 Win Mag as direct competition against Weatherby’s then famous 257 Magnum. With similar case capacity, a slightly larger bullet, and similar working pressure, Winchester hoped its new Magnum would garner a good share of sales to those who believed in Roy Weatherby’s high-velocity, light bullet concept for big-game hunting. When loaded to the same pressure using the best modern propellants, compared to the much smaller 6mm-284 Norma and 6mm-06 rounds, the performance edge for the 264 Win Mag is 120 fps with typical hunting bullets. Winchester used some interesting design features to try to gain better accuracy and performance from the case, the original factory 140-grain load used a bullet that stepped down from full diameter to under bore size forward of the cannelure. This allowed it to use a short chamber throat without giving up usable capacity. This also resulted in no end of problems for handloaders and ammunition manufacturers who needed or wanted to use conventional 6.5mm bullets. As was a host of standard belted–magnum cartridges, this case was derived from the circa 1912, 375 H&H.