The 6.5-284 is based on the .284 Winchester case necked-down to accept .264" (6.5mm) diameter bullets. This is a unique, rebated rim case used for no other factory produced cartridge.

There are no standards for wildcat cartridge dimensions, but these are provided for the 6.5mm-284 in the sixth edition of the Hornady Handbook of Cartridge Reloading: Bullet diameter .264"; Maximum case length 2.170" (trim to 2.160"); Maximum cartridge overall length 2.80"; Rim diameter.473"; Base diameter .500"; Shoulder diameter .475"; Shoulder angle 35 degrees; Neck diameter .295".

Unfortunately, the .284 Winchester parent cartridge is dying and brass is not widely distributed. The .284 is a 7mm caliber, so one pass through a 6.5-284 resizing die should do the job. Whether it is worth owning a wildcat rifle to shoot a 1/2 millimeter smaller diameter bullet from the same case is the question.

The Hornady Handbook is a good source for 6.5mm-284 reloading data. They recommend VIHT N-165, IMR 4831, Win. WMR, and AA 3100 powders with the heavier 129 and 140 grain bullets for which a cartridge of this capacity would seem best suited.

Win. WMR powder gave top performance with both the 129 and 140 grain Hornady bullets in the 6.5-284. With the 129 grain bullets, 44.8 grains of WMR powder gave a MV of 2500 fps. A maximum load of 52.9 grains of WMR drove the same bullets to a MV of 2900 fps, the only powder listed that exceeded 2800 fps at safe pressure levels in Hornady testing.

Using Hornady's 140 grain bullets in front of 43.6 grains of WMR yielded a MV of 2400 fps. And a maximum load of 49.7 grains of WMR gave the 140 grain bullets at a MV of 2700 fps. Winchester cases and Federal 210 primers were used for all of these Hornady loads, which were chronographed in a 24" rifle barrel.

It is interesting that the top velocities listed for the 6.5mm-284 are identical to the top velocities for the .260 Remington (6.5mm-08) with the same bullet weights in the Hornady Handbook. The 6.5-284 just burns more powder to get there.

Note: Another article about the 6.5mm-284 can be found on the Rifle Cartridge Page.