jwp,
While some writers of the day mentioned the .264 might burn out barrels quicker than other rounds (especially Elmer Keith, who hated the entire concept of the cartridge) I suspect the two major reasons it didn't do all that well were:
1) The introduction of the 7mm Remington Magnum in 1962, only three years after the .264.
Back then muzzle velocity and bullet weight were the major measures of a big game round. Very few hunters shot beyond 400 actual yards (though plenty bragged about longer ranges), and muzzle velocity has far more influence on trajectory to 400 than ballistic coefficient. Very few hunters used "premium" bullets, because the Nosler Partition was the only one available and had to be handloaded, thus more bullet weight was considered necessary for big game, especially game larger than deer. The 7mm offered 150 and 175 grain factory loads, both heavier than the .264's 140 grains.
Also, various enthusiastic wildcatters (including influential gun writer Warren Page) had been fooling with 7mm magnums for years. Weatherby already offered a commercial version, but both Weatherby rifles and ammo were expensive. The new Remington 700 the 7mm Magnum appeared in had a kind of toned-down Weatherby-style stock, but both the rifle and ammo cost a lot less than Weatherby's. The Remington combination fulfilled an already existing demand, at a time where even most rifle loonies weren't clamoring for a 6.5mm magnum, since at the time 6.5mm was considered a rather weird "foreign" caliber.
2) Eventually reports appeared that the .264's factory 140-grain load often didn't reach the listed velocity of 3200 fps, even in the long-barreled Model 70 "Westerner." The number 6 Speer manual, published in 1964, published a list of factory ammo chronographed in their lab. In the 26-inch barrel of a Westerner, Remington 140-grain ammo got 3025 fps and Winchester 140's 3139 fps. In the same list, Federal, Remington and Winchester 130-grain .270 Winchester ammo all came reasonably close to the advertised velocity of 3140 fps--from a 22-inch barrel.
There also weren't any high-BC hunting bullets back then; instead there were basic flat-based, softpoint spitzers. As a result of the similar velocities, the .264 didn't shoot noticeably flatter than the .270 at typical hunting ranges. I know this partly because, years later, I owned and hunted with a .264 Westerner.
Between the established .270 Winchester and the new, popular 7mm Remington Magnum the .264 didn't have much chance. Now it might, but powders have advanced so much the 26 Nosler and 6.5-.300 beat the .264's velocities pretty easily.
