Simpson took this pronghorn in New Mexico with a T/C Encore rifle in 6mm-06 and the Swift 90-grain Scirocco bullet.

For many years the 6mm-06 and other wildcats of the same caliber with similar appetites for powder were less than practical, simply because with the exception of military-surplus H4831, the burn rates of powders available to handloaders were too fast. This no longer is true. In addition to the old standby H4831, we have powders such as IMR-7828, Reloder 22, Norma MRP, Hodgdon H1000, Western Powder’s Magnum , VihtaVuori N160 and Hodgdon Retumbo, all quite suitable for use in the Big Sixes.

Cases for the 6mm-06 are easily formed by squeezing down the necks of .30-06 brass with a 6mm-06 full-length resizing die. If you experience unacceptable case loss when doing so, the solution is to run the .30-06 cases through a full-length resizer in 6.5-06 or .25-06 before necking them on down to 6mm. This intermediate step, I might add, is never necessary when forming cases from .270 Winchester or .25-06 brass.

Regardless of the case you start out with, neck diameter--with a bullet seated--must be held to 0.290 inch or smaller. Should a batch of formed cases exceed that dimension, their neck walls will need to be thinned by the necessary amount by reaming or outside turning.

Maximum case length of 2.494 inches is the same as for the .30-06, which means that cases formed from .270 Winchester brass will need to be trimmed back by a slight amount.

I am unaware of any pressure-tested load data that has been published for the 6mm-06, but since its case capacity is quite close to that of the .240 Weatherby Magnum and the 6mm-284, starting loads for those can be used.

The chamber of the Weatherby Mark V in .240 Magnum is not freebored like it is for other Weatherby cartridges, but its throat is a bit longer than is commonly seen in rifles chambered for other 6mm cartridges. To be on the safe side, starting loads published for the .240 Magnum should be reduced by 5 percent when used in the 6mm-06.

Continuing on with a note of caution, starting loads found in the Hornady manual for the 6mm-284 should also be reduced by 5 percent when used in the 6mm-06.

I compared the water capacity of the 6mm-06 formed from .25-06 cases from Remington with the .240 Magnum case from Weatherby and 6mm-284 cases formed from .284 brass made by Winchester. When all were filled to the brim with water, average gross capacity of the 6mm-06 is a half grain more than for the .240 Magnum and 2.3 grains less than for the 6mm-284.

This gives the 6mm-284 a slight edge over the other two, but only when it is used in a rifle with an action long enough to allow seating the heavier bullets out of its powder space. More often, that cartridge is used in a short-action rifle in which deep-seating of bullets is required to allow cartridges to fit into the magazine, which reduces its net powder capacity to about the same as the .240 Magnum and the 6mm-06.

Coming up with a rifle in 6mm-06 is quite easy. Best bet is an action made for the .30-06 family of cartridges, since no modifications will have to be made.

I once owned a rifle in this caliber built on the 1903 Springfield action, but my present 6mm-06 rifle is a T/C Encore single-shot with a 26-inch barrel, built by the Thompson/Center custom shop. I have used it to take several deer, but my longest shot to date was a laser-ranged 356 yards on a pronghorn antelope in New Mexico.