Useful Wildcat Hunting Cartridges

(Includes: 6x45mm, 7mm-300 Weatherby, 8mm-06, .35-30, .416 Barnes)

By Chuck Hawks

A "wildcat" is a cartridge that is not standardized by the American SAAMI or European CIP associations and is not produced by one of the major loading companies that belong to either of those organizations. Wildcats are typically based on a modified existing cartridge case and seek to fulfill some special purpose or fill a niche that the wildcat's creator feels is inadequately addressed by existing standard cartridges. A wildcat cartridge is typically created by taking an existing cartridge case and necking it up or down to accept a different diameter bullet, shortening it, blowing it out to decrease body taper, changing the shoulder angle and shortening or lengthening the neck. Decreasing the body taper, moving the shoulder forward and increasing its angle, and shortening the neck are all methods commonly used to increase powder capacity and therefore performance.

There are thousands of wildcat rifle cartridges, most of which are virtually unknown except to their creators and possibly a few friends. Most are superfluous and have no practical advantage over comparable standardized cartridges. Many wildcats achieve improved performance, compared to a similar standard cartridge, simply because they are being loaded to a much higher, sometimes dangerously high, maximum average pressure (MAP). Often their creators have no idea at what pressure their offspring is operating and assume it to be safe merely because they haven't (yet) blown up their rifle.

Although not generally a fan of wildcat cartridges, I have to admit that there have been some interesting and useful wildcat creations in addition to those introduced on Guns and Shooting Online. (G&S Online wildcats include the .270 Marlin Express, .270 T/C, .338 Marlin Express and .338x57 O'Connor.) I intend to examine a few of those in this article. The reference I have relied on most in this endeavor is the 9th Edition of Cartridges of the World by Frank C. Barnes and edited by M. L. McPherson. Anyone interested in rifle or handgun cartridges should own a copy of this book.

6x45mm (6mm-223)

The 6x45mm is created simply by necking-up 5.56x45mm NATO or .223 Remington brass to accept standard 6mm (.243") bullets. It provides an inexpensive way to convert AR-type .223 caliber rifles to a more powerful caliber. It is also reasonably popular in Thompson/Center's single shot pistols and carbines. The 6x45 has military potential as a replacement for the 5.56mm NATO due to its greater stopping power and penetration, although it is unlikely ever to be adopted as a service cartridge.

While no powerhouse, the 6x45 is a useful varmint/small predator cartridge and a much better cartridge than the .223 for those who insist on tormenting deer with AR-type semi-automatic rifles. It can drive a 90 grain bullet to a muzzle velocity around 2700 fps, similar ballistic performance to the 6mm PPC, and feed reliability is not an issue in repeating rifles.

Accuracy is usually excellent (when fired from bolt action and single shot rifles), trajectory is reasonably flat, recoil and muzzle blast are very light. These factors make the 6x45 a viable choice for young, infirm or very sensitive shooters. .223 brass is both widely available and inexpensive, and RCBS offers reloading dies in 6x45mm. The .243 Winchester is a better all-around choice for most shooters and hunters, but there is a niche for the 6x45mm.

7mm-300 Weatherby Magnum

This wildcat would seem to have been a natural for adoption by Weatherby years ago. It is merely the .300 Weatherby Magnum case necked-down to accept .284 inch bullets. The result is a full (.375 H&H) length cartridge similar to the 7mm STW. The 7mm-300 is, of course, only adaptable to rifles with full length magnum actions such as the Weatherby Mark V Magnum action.

Naturally, the 7mm-300 Wby. retains the trademark double radius Weatherby shoulder. It is a belted case with a standard magnum rim diameter of .532 inch, a base diameter of .511 inch, and a shoulder diameter of .490 inch. The case length is .2.825 inches and the overall cartridge length is 3.65 inches.

This is a very powerful all-around big game cartridge capable of driving its bullets about 150 fps faster, on average, than the standard 7mm Weatherby Magnum. A 150 grain bullet can be launched at a MV of around 3450 fps, a 160 grain bullet at around 3350 fps, and a 175 grain bullet at around 3250 fps. These are high pressure loads intended for use only in very strong rifles such as the Weatherby Mark V. Naturally, long 26-28 inch barrels are recommended to achieve such velocities. Well constructed bullets at these velocities will do for all North American big game.


This useful wildcat came about due to a shortage of 8x57JS ammunition and brass in the U.S. during and after WW II. Since there was plenty of .30-06 brass about, it was natural to re-chamber 8mm Mauser rifles to 8mm-06.

The 8mm-06 wildcat is merely the .30-06 case necked-up to accept .323" bullets, without other changes. The rim diameter remains .473 inch, the head diameter is .4707 inch, the case length is 2.494 inches long, and the overall cartridge length is 3.25 inches. The shoulder remains 17.5 degrees.

In Europe the 8mm-06 would be called the 8x63S. It is very similar in performance to the European 8x64S Brenneke, and makes a good all-around big game cartridge.

While there are not as many bullet weights available in North America for 8mm cartridges as there are for .30 caliber cartridges, there are enough. The most common of these include 150, 170, 180, 200, and 220 grain. All of the major bullet makers, including Barnes, Hornady, Nosler, Sierra, Speer, and Swift (among others) offer .323" bullets to reloaders.

For hunting most species of deer, antelope, sheep, and goats with the 8mm-06, bullets of 150 grains (SD .205) at a MV of 2850-2950 fps are probably a good choice. For bigger animals like caribou and large black bear, and for use on mixed bag hunts, a good 170-180 grain bullet (SD .233-.247) at about 2700-2800 fps would probably be a good all-around choice. For large animals like alg, elk, kudu, moose and the great bears bullets of about 200 grains (SD .274) can be driven to MV's in the 2600+ fps range and would seem a reasonable choice.

Basically, the 8mm-06 can do anything the .30-06 can do as a big game rifle. Which, when you think about it, is saying quite a lot.


This old but useful wildcat is based on the .30-30 Winchester case necked up to accept .358 inch bullets. It is not a new idea, having first appeared some time around 1900. It is a worthwhile way to salvage worn .32 Winchester Special barrels, and presumably adds killing power for use on game larger than deer.

Unlike rimless .35 caliber cartridges based on necked-up .308 and .30-06 cases, which sometimes have headspacing problems due to an inadequate amount of shoulder, the .35-30 headspaces on its rim, just like the .30-30 and .32 Special parent cases. This makes the .35-30 a pretty good cartridge for traditional lever action rifles, better in some respects than the rimless .35 Remington. The .35-30 has about 14% less powder capacity than the .35 Rem., but a much longer neck so that heavier bullets do not intrude into the powder space.

The basic dimensions of the .35-30 are as follows. The shoulder angle is unchanged from the 14 degree 31 minutes of its parent case. The rim diameter is .506 inch, the base diameter is .4219 inch, and the shoulder diameter is .4014 inch. Case length is 2.04 inches, and overall cartridge length is about 2.55 inches. Blunt round nose or flat point bullets must be used in rifles with tubular magazines.

The performance of the .35-30 in the field is similar to that of the .35 Remington from 20" carbine length barrels. A 180 grain bullet can be driven to a MV of around 2100 fps; a 200 grain bullet can be driven to a MV of about 1925 fps, and a 220 grain bullet to a MV of about 1850 fps. The .35-30 has proven to be an able deer and black bear cartridge with quick opening 180-200 grain bullets, and can account for larger game at close range using the heavier 220 grain bullet.

.416 Barnes

The late Frank Barnes, author of the reference book Cartridges of the World, designed this number. His basic premise was that a .416 caliber cartridge designed for use on the larger species of North American game (rather than thick-skinned African game) might have some appeal. Barnes made his new cartridge adaptable to several existing popular rifles, and based it on brass that was widely available, a most logical and commendable approach more wildcatters should emulate.

Frank Barnes chose the .45-70 case as the starting point for his new cartridge, and necked it down to accept standard .416 inch diameter bullets. The .416 Barnes is a rimmed bottleneck case with a modest shoulder. The rim diameter of the basic case in .608 inch, and the base of the case body is .505 inch in diameter. The case body tapers to a diameter at the shoulder of .484 inch. The case length is 2.112 inches, and the cartridge overall length is 2.95 inches.

The .416 Barnes is adaptable to any rifle that can handle the higher pressure versions of the .45-70 cartridge. The Marlin Model 1895 lever action, for example, immediately comes to mind as an excellent basis for a .416 Barnes rifle. Most single shot and double rifles, as well as some bolt action models, could also be adapted to the .416 Barnes cartridge.

The .416 Barnes can drive a 300 grain bullet to a MV of about 2300 fps, and a 400 grain bullet to a velocity of around 2100 fps. This provides somewhat greater power than the storied .405 Winchester, and is adequate for all North American game. In a Marlin 1895 rifle the .416 Barnes is a stopper comparable to the .450 Marlin Magnum with somewhat better penetration for any given bullet weight. This cartridge should definitely be given production status by Marlin.


The cartridges described above are not by any means the only useful wildcats, but they are examples of practical wildcats that actually fill a real need. The 7mm-300 Weatherby Magnum and .416 Barnes would make practical additions to the factory loading lists.

The 8mm-06 and .35-30 also fill definite needs and are excellent cartridges in their own right. Because the similar .270 Winchester, 8x57JS Mauser and .35 Remington are already established it is unlikely that any of this trio of useful wildcats will be adopted by one of the major ammunition companies any time soon. But every year intrepid hunters and reloaders will continue to use them to fill their big game tags.

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Copyright 2003, 2012 by Chuck Hawks. All rights reserved.