450 Ashurst From Unintended Consequences by John Ross.
".450 Ashurst," Kearns said immediately. "Full length .375 H&H case necked up to .458 caliber and blown out straight. Holds more powder than the .458 Winchester magnum, but only if you've got an action with a long magazine. Google produces pretty much nothing -- one thread on Cast Boolits confirming that John Ross didn't just make the name "Ashurst" up like authors sometimes do.
Jack Ashurst lived in Grangeville, Idaho, and took over Lyman McCrea's gunshop and cartridge line about 1941. He dropped the McCrea cartridge designs for his own. He had four .25 calibers, based on the .22 Savage HP, the .30-30, the .30-06 and the .275 H&H Magnum cases, and a .270, .280, 7MM and .300 cartridge series all based on the .300 H&H Magnum case. The cases featured the short necks and abrupt shoulders typical of wildcats of the period, although several of them retained the body taper of the parent cases. The usual blistering velocities were claimed for these creations. This from Wildcat Cartridges by Richard F. Simmons. I think P.O. Ackley described some Ashurst Handbook for Shooters and Reloaders. However, neither list a 6mm Ashurst.
