Yes, a 30-378 is a 378 Weatherby case that is necked down to 30 caliber. It was a wild-cat cartridge when Roy Dunlap built this rifle, but now its a factory caliber available from Weatherby. Although most Brevex actions were used for Big Game calibers, they were used any time a Magnum length action was required. Sales in the U.S. were from Tradewinds. They were the sole Importer, and the actions were reasonably priced. During the mid 50s through the 70s, Brevex was the only MAGNUM action available. There were only approximately 450 actions made. Here is a 1955 ad.