The parent case is the old .284 Winchester. It has a 30/06 size rebated head; and the fatter body of the case is slightly smaller than the 7 Rem Mag ahead of the belt. It was originally designed to put .280 Reminton performance in a short action rifle. But the 6MM-284 wildcat can barely be used in a short action without compromise; and the .257, 6.5, and .270 wildcats definitely need the long action to work.

The case has about the same capacity as the 30/06, but with a shorter fatter powder column. It represents about the maximum case capacity that can be effeciently utilized in the 6MM bore - a little above that of the .240 Weatherby. It also has turned out to be one of the most inherently accurate cases ever developed for long range shooting. The 6.5-284, while posting performance figures similar to the .270 Winchester, is rapidly becoming the overwhelming favorite of the 1,000 yard competition shooters. I have personally seen 10 shot groups of 2.5" at 600 yards shot with one of these guns.