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6mm-06 Wildcat

by Layne Simpson   |  January 4th, 2011 1

The 6mm-06 pushes small-bore performance to the max.


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.

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10 GREAT 6MM-06 LOADS

Bullet Bullet Weight (gr.) Powder Charge Weight (gr.) Muzzle Velocity (fps)
Nosler Ballistic Tip 55 H414 52.0 3,817
Sierra Hollow Point 75 V-N160 53.0 3,644
Sierra Hollow Point 80 Magnum 55.0 3,382
Barnes X-Bullet 85 IMR-4350 49.0 3,479
Swift Scirocco 90 H4831 53.0 3,428
Hornady SST 95 RL-22 52.0 3,364
Nosler Partitiion 100 IMR-7828 52.0 3,273
Sierra GameKing 100 AA-3100 50.0 3,236
Speer Grand Slam 100 H4831 51.0 3,215
Speer Soft Point 105 RL-22 51.0 3,210
Notes:All powder charges are maximum and should be reduced by 15 percent for starting loads. Velocities are averages of five or more rounds clocked at 12 feet from the muzzle of a 26-inch T/C Encore rifle barrel. Cases were formed by necking down Remington .25-06 brass and Remington 91⁄2 primers were used.

The deer and the antelope were taken with a Swift 90-grain Scirocco, loaded to 3,450 fps. I have yet to come up with a reason for switching bullets. When zeroed three inches high at 100 yards it strikes about four inches high at 200, dead on at 300 and low by about half the body depth of a whitetail deer at 400 yards, where it is still packing close to 1,200 ft.-lbs. of punch.

The 6mm-06 is far too much cartridge for prairie dogs, but its ability to push bullets of high ballistic coefficient at high speeds makes it a great candidate for shooting rockchucks and eastern groundhogs at extremely long ranges.

Choosing between the 6mm-06, the 6mm-284 and the .240 Weatherby Magnum is easy. If you prefer to use factory ammunition, then the .240 Weatherby Magnum is your cup of tea. If you handload and prefer a short-action rifle then the 6mm-284 is the way to go.

The 6mm-06 makes more sense in a long-action rifle, and .30-06 cases are usually easier to find and less expensive than .284 Winchester or 6.5-284 cases.

Everything including bullet weight, barrel length and the pressures to which they are loaded being equal, I find the 6mm-06 to be about 300 fps faster than the .243 Winchester and 200 fps faster than the 6mm Remington and .243 WSSM. Whether or not that gain in velocity justifies owning a rifle chambered for a wildcat cartridge is for the fellow who is spending the money to decide.

Warning: The loads shown here are safe only in the guns for which they were developed. Neither the author nor InterMedia Outdoors assumes any liability for accidents or injury resulting from the use or misuse of this data. Shooting reloads may void any warranty on your firearm.

  • okie2

    you did not show a 70 grain bullet but my 6-06 ackley will shoot then over 4200 fps.
    So the 240 weatherby or the 6-284 is no match for the 6-06 ackley

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