The 6mm-284 and 6mm-06
By Chuck Hawks
The 6mm-284 and 6mm-06 offer basically the same level of performance. Both will push .243" bullets about 100-150 fps faster than the 6mm Remington at the same pressure. To do so they burn 20-25% more powder and produce more muzzle blast and recoil. The 6mm-284 and 6mm-06 are both wildcats, use the same bullets, and have similar case capacities. Ballistically, what one can do the other can also do. In performance, both of these wildcats are pretty close to the .240 Weatherby Magnum, which is a cartridge standardized by the SAAMI and for which rifles and factory loaded ammunition are in regular production.
Like all wildcats, there is no official SAAMI pressure limit for either cartridge, nor is there a set cartridge overall length. In this situation, the chambers of custom rifles can and do vary, which affects pressure and velocity. It is one of the inconveniences of owning a wildcat. Also, reloading data should be viewed with suspicion. Accept data only from reliable sources, which in this case means the major published reloading manuals. Beware, there are some pretty iffy loads circulating out there, particularly on the Internet.
The primary difference between the two cartridges is that the 6mm-284 is a short action caliber, and the 6mm-06 requires a standard length action. If you are pining for a custom 6mm rifle with greater performance than the 6mm Remington and it is a short action rifle that is to be the basis for your conversion, the 6mm-284 is for you. On the other hand, if it is a standard length action you intend to convert, then the 6mm-06 is a better choice.
The 6mm-284 is one of the few wildcat cartridges to become more popular than its parent cartridge. When the .284 Winchester was introduced, wildcatters had a field day necking it up and down. .243" diameter bullets proved to be a good choice for long range shooting, and today I understand that reloading dies in 6mm-284 outsell dies for the regular .284 Winchester. Evidently the 6mm-284 fills a need. It relates to the 6mm-06 as the .284 Winchester relates to the .280 Remington.
What will happen to the 6mm-284 if the .284 Winchester is discontinued and .284 brass becomes unavailable? This is always a problem for the rare popular wildcat based on an unpopular parent case. But perhaps before that occurs Winchester (or someone) will adopt the 6mm-284 as a factory cartridge.
Producing a 6mm-284 case is simply a matter of running .284 Winchester brass through a 6mm-284 forming die. Trim to a length of 2.155" if necessary. Naturally, the 6mm-284 is at its best with slow burning powders. These are necessary to achieve the high velocities of which the cartridge is capable, and to keep pressures within reason.
With 75-85 grain bullets the 6mm-284 makes an awesome varmint cartridge, similar to the .240 Weatherby. The Hodgdon Data Manual 26 shows that 51.0 grains of H4831 can drive an 80 grain varmint bullet to a MV of 3397 fps; 55.0 grains of H4831 delivers a MV of 3683 fps with the same bullet.
Like the .240 Weatherby, the muzzle blast and report are a problem for most varmint shooters, not to mention the accelerated barrel erosion if the shooting gets fast and furious. As varmint cartridges, the .243 Winchester or 6mm Remington are probably better choices.
The 6mm-284 is at its best with the heaviest bullets in the caliber, those weighing 90 grains and up. The 100 grain and 105 grain spitzer bullets are a particularly good choice for medium size big game at long range.
According to the Hodgdon Data Manual 26 the popular 100 grain spitzer bullets can be driven to muzzle velocities of 3011 fps with 46.0 grains of H4831. 49.0 grains of the same powder gives a 100 grain bullet a MV of 3207 fps.
Unlike many reloading manuals, the Hodgdon Data Manual gives pressure information for many loads. In the case of the H4831 maximum load for the 100 grain bullet at 3207 fps the pressure listed was 49,100 cup.
At 3200 fps the muzzle energy of a 100 grain bullet is 2274 ft. lbs. At 200 yards Hornady's figures for their 100 grain Spire Point bullet are 2651 fps and 1561 ft. lbs. The trajectory of that bullet at a MV of 3200 fps looks like this: +2.5" at 100 yards, +3" at 150 yards, +2.4" at 200 yards, and -3" at 305 yards.
One problem that the wildcat 6mm-06 will not have any time soon is a shortage of .30-06 brass to neck down. Unlike the .284, the 6mm-06 is based on the most popular cartridge in the world. Again, it is a simple process to neck down 30-06 (or even better .270 Winchester) brass to accept .243" diameter bullets. The result is a 6mm-06 case.
The 6mm-06 became popular shortly after the introduction of the .243 Winchester in 1955, which made a good selection of 6mm bullets widely available to reloaders and wildcatters. Certainly experimenters had necked down .30-06 and .270 Winchester cases to accept 6mm bullets long before 1955, but it was the .243 Winchester that really brought the .24/6mm caliber into the limelight. The 6mm-06 has gained in popularity ever since, and the introduction of ever slower burning powders has made this once seriously over-bore cartridge a viable proposition.
I have had a modicum of experience with the 6mm-06 myself; this was many years ago when I was still in the USAF and a roommate owned a 6mm-06 rifle. I must say that at 200 yards the bullet seems to get there at nearly the same instant the gun goes off, much like with the .257 Weatherby Magnum. (The actual time of flight to 200 yards, according to the Speer Reloading Manual, is 0.2022 seconds for a 105 grain spitzer bullet at a MV of 3200 fps.)
Like the 6mm-284 and the .240 Weatherby Magnum, which have nearly identical case capacity, the 6mm-06 is at its best with the heaviest bullets in the caliber. The 100 grain and 105 grain spitzer bullets are a particularly good choice for medium size big game at long range.
The 105 grain bullet can be driven to a MV of around 3150 fps. 6mm-284 data can be used as a starting point for working up 6mm-06 loads. As always, and especially with a wildcat cartridge, start with the minimum load and work up slowly, checking carefully for signs of excess pressure. Verify results with a chronograph, and stop testing immediately if you get unexpected velocities. (If you are reloading for a wildcat cartridge, a chronograph is a necessity.)
At 3100 fps the ME of a 105 grain bullet is about 2240 ft. lbs. The 200 yard figures are 2663 fps and 1653 ft. lbs. The trajectory of that load looks like this: +1.5" at 100 yards, +2.3" at 200 yards, 0 at 258 yards, and -3" at 305 yards.
The 6mm-284 and 6mm-06 are among the most popular and most useful wildcat cartridges. In case capacity and performance they are similar to the commercially available .240 Weatherby Magnum. They are excellent long range cartridges for all small to medium size species of big game. I would not be too surprised if a major ammunition company someday domesticated one or both.
Copyright 2002, 2012 by Chuck Hawks. All rights reserved.