The .30-06 Springfield is the parent case of the .25-06, 6.5mm-06 and the .270 Winchester, all of which are pretty similar both ballistically and visually. Had the 6.5mm-06 been commercially adopted first, the other two would not have been necessary.

6.5mm-06 brass is most easily produced by necking-up the .25-06 Remington case to accept .264" (6.5mm) diameter bullets. The .25-06 uses .257" bullets, so one pass of a .25-06 case through a 6.5-06 resizing die should do the job. .25-06 brass is widely distributed, a convenience for 6.5-06 reloaders.

As an alternative to necking-up the .25-06 case is necking down the .270 Winchester case and trimming to length. Whether it is worth owning a wildcat rifle to shoot bullets of the same weight that are 0.013" smaller in diameter from the same case is the question. It is hard to see what the 6.5mm-06 wildcat can do that the .270 Winchester cannot.

Anyone with a 6.5mm-06 rifle, especially if using .25-06 or .270 brass to form 6.5-06 cases for reloading, should be very careful not to mix cartridges for the two calibers. Shooting a .270 Winchester cartridge in a 6.5-06 rifle would cause dangerously high pressure that could blow up the rifle. Alternatively, shooting a 6.5mm-06 cartridge in a .25-06 rifle could be equally hazardous.

If chamber and cartridge specifications are perfect the larger caliber cartridge should not chamber in the smaller caliber rifle, but the real world is not always perfect. That is why Remington found it necessary to move the shoulder of the .280 slightly forward and Winchester found it necessary to move the shoulder of the 7mm WSM slightly forward. In both cases that was done to prevent the 7mm cartridge from chambering in rifles intended for the nearly identical .270 caliber cartridge. Great care should always be taken when reforming cases that look so similar to each other.

The dimensions for wildcat cartridges are not fixed, but these are provided for the 6.5mm-06 in the sixth edition of the Hornady Handbook of Cartridge Reloading: Bullet diameter .264"; Maximum case length 2.494" (trim to 2.484"); Maximum COL 3.340"; Rim diameter.473"; Base diameter .470"; Shoulder diameter .441"; Shoulder angle 17 degrees, 30 minutes; Neck diameter .298".

Being a wildcat, there is no SAAMI MAP for the 6.5-06. However, the MAP for the .270 Win. is 52,000 cup and the MAP for the .25-06 is 53,000 cup. It would be sensible to keep the MAP of the 6.5mm-06 to similar levels.

The Hornady Handbook is a good source for 6.5mm-06 reloading data. They recommend VIHT N-165 and H 4831 powders for their 129 and 140 grain bullets.

42.6 grains of VIHT N-165 powder gave a MV of 2600 fps with the 129 grain Hornady bullets. A maximum load of 52.9 grains of VIHT N-165 drove the same bullets to a MV of 3000 fps.

Using Hornady's 140 grain bullets in front of 43.6 grains of VIHT N-165 yielded a MV of 2500 fps. And a maximum load of 50.4 grains of VIHT N-165 gave the 140 grain bullets at a MV of 2800 fps. Hornady cases and Winchester WLR primers were used for all of these Hornady loads, which were tested in a 24" rifle barrel.

It is interesting to note that, comparing data from the Hornady Handbook, the top velocities listed for the 6.5mm-06 with 129 and 140 grain bullets are 100 fps slower than the top velocities for similar weight bullets in the .270 Winchester.

On the other hand, the 6.5mm-06 will drive 100 grain bullets roughly 100 fps faster than the .25-06, and 120 grain bullets about 50 fps faster.

Note: Another article about the 6.5mm-06 can be found on the Rifle Cartridge Page.