Like all new products, the .256 Win. Mag. hit the market with a resounding boom, but fizzled out almost immediately. That was in 1960 and a lot of other new cartridges have come and gone in the intervening years. The .256 was the .357 Mag. necked down to take a .25 caliber bullet weighing 60 grains. Velocity was quoted at 2200 fps from an 8-inch barrel. It was supposed to be a light varminting cartridge and sort of a modern version of the old .25-20 Win. I believe the .256 was intended to be a specialty handgun cartridge, but it adapted well to short rifles and carbines. At about the same time in handgun history, Remington was working with S&W and the .22 Jet. Several different wildcats were also drawing a good bit of attention.
In order to fire the .256 cartridge, two new major firearms appeared on dealer's shelves. The Hawkeye was a single-shot handgun on the Blackhawk frame by Ruger. The other was a modernized lever-action rifle by Marlin. For reasons I don't completely understand, neither gun caught fire and only limited numbers were ever made and sold. Although you could get .256 T/C Contender barrels for a good while and even some M1 Carbine clones, the whole concept just plain flopped. I shot a Hawkeye extensively one day and thought it was pretty neat. The late Bob Milek once wrote a lengthy piece on the .256 with precious little good to say about it. I always respected his judgment. Ammo got hard to find, no new guns were offered and eventually the makers just sort of sighed and said "never mind."
Then something unusual happened that caused me to believe that the timing of the whole .256 debacle may have been way off. I bought a used gun book from a midwestern dealer and it was delivered via U.S. mail. Opening the package, I found the book as advertised. An unexpected bonus felt out of the back pages. It was an advertising leaflet roughly 6x6" announcing the introduction of four new revolvers chambered for the new .256 Win. Mag. cartridge. No less of a revolver maker than Colt's Patent Firearms Mfg. Co. was announcing a 7 ½" Single Action Army, a 12-inch Buntline, a 6-inch Python and a 6-inch "Two-Fifty-Six." If any of these guns really saw the light of day, I would be surprised. I have never heard of them and can find no reference to them in my reference library. An Internet search repeats and re-repeats the rumor of their existence.