6.5-284 Winchester

When I left Cooper Arms in the summer of 2008, the company had just begun to transition away from single-shot varmint rifles in favor of the biggame hunting market.

- Rob Behr

At the time, Cooper offered more than 60 different chamberings spread among three single-shot rifles, a pair of rimfire actions and the Model 52 repeater. My favorite was the Model 22, with its robust, three front locking lugs and broad Sakostyle extractor. The actions are tough, stiff and accurate. Best of all, it came in the most consistently accurate cartridge the company offered, the wildcat 6.5-284 Winchester.

When Winchester released its .284 cartridge in 1963, it was intended to provide .270 Winchester performance in a modern lever action called the Model 88, and the trim semiautomatic Model 100. The .284 case body was broad, measuring .500 inch just above the extractor groove and tapering to .475 inch at the shoulder. Winchester’s engineers wisely added a rebated .473-inch rim to the cartridge, making it readily adaptable to most popular actions. With 66 grains of water capacity, the .284 Winchester was within one grain of the .270 Winchester, but it could be chambered in short-action rifles. On paper, the .284 looked like another homerun for Winchester, but it failed to find a place with shooters. Savage and Browning also offered the chambering for a time, but finding the same demand as Winchester, quietly dropped the cartridge from their lineups.

The .284 Winchester’s main problem, it was said, was its case length. At 2.170 inches, it was .155 inches longer than the .308 Winchester, the cartridge that set the size parameter for short-action rifles. In order to load cartridges into a standard short-action magazine, the maximum cartridge length had to be no more than 2.800 inches. This meant the .284 was tied to lighter, shorter bullets. Longer bullets had to be seated deeply into the case at the cost of powder capacity and velocity. For Winchester, the cartridge proved to be a commercial flop, but for wildcatters it was a gift.