The Universal M1 Carbine was chambered in .256 Winchester also.
http://www.m1carbinesinc.com/carbine_Universal256.html
quote> Only five firearms are known to have been chambered for this cartridge, none of which are currently manufactured.
Ruger Hawkeye single shot pistol (introduced 1961)
Marlin Model 62 Levermatic rifle (introduced 1962)
Rex Merrill Sportsman single shot pistol (interchangeable .256 Win Mag barreled upper)
Thompson/Center Contender single shot (interchangeable .256 Win Mag barrel)
Universal .256 Winchester Magnum carbines (introduced 1963) <end quote
A friend I shoot with has a bolt action and an AR rifle both modified for the .256 Winchester magnum cartridge. He has the dies and makes his cases out of 357mag brass. They shoot really well.