A wildcat cartridge, or wildcat, is a custom cartridge for which ammunition and firearms are not mass produced. One source of gunsmithing equipment has a library of over 6,000 different wildcat cartridges for which they can make chamber reamers.¹

Development of a wildcat

Often, wildcats use the case of a commercially sold cartridge that has been modified in some way to alter the cartridge's performance. Barrels for the caliber are originally manufactured by gunsmiths specializing in barrel making. Generally the same makers offer reloading dies for the new cartridges (based on the dimensions of the chamber reamers used for the barrels). Since the most difficult to manufacture part of a wildcat is the barrel, most wildcats are developed by or in association with custom barrel makers. Ammunition is handloaded, using modified parent cases and the gunsmith-provided wildcat dies. Generally the supplier of the barrel or dies will also provide the buyer with basic reloading data, giving a variety of powders, charge weights, and bullet weights that can be used for developing loads. Experienced handloaders will take this data and very carefully develop a load, starting with minimum loads, perhaps switching to similar but unlisted powders, and carefully work up a load for their needs. Wildcats are not for the casual shooter; the work and skill required relegates them to the world of dedicated and experienced shooters.

Wildcat cases and cartridges can be found for sale, but only from small makers. Larger manufacturers stay away from wildcats because there are no established CIP (Commission Internationale Permanente Pour L'Epreuve Des Armes A Feu Portatives - Permanent International Commission) nor SAAMI standards, which causes liability concerns.

Wildcat goals and methods

Wildcat cartridges are developed for many reasons. Generally, the goal is to increase some characteristic of a commercial cartridge in a given context. Higher velocities, greater energy, better efficiency, and greater consistency (which yields greater accuracy) are the top reasons. One of the most fertile breeding grounds for wildcats is the sport of handgun metallic silhouette shooting, which pushes the limits of cartridge ballistics from short barrels.² In using autopistols for hunting or competitive shooting, improved feeding of softnose or hollowpoint bullets is also an issue; the bottlenecked .45/38, for instance, was created because the straight-cased .45 ACP had trouble feeding hollowpoints.³

• Higher velocities are often obtained by increasing the case capacity, or reducing the caliber.
• Greater energy can be attained by increasing the caliber or the case capacity.
• Better efficiency is often obtained by increasing the shoulder angle, shortening the case, and reducing case taper (see internal ballistics).
• Greater consistency is attained by tuning the case capacity to a certain bullet diameter, weight, and velocity that give consistent results.
• Fewer feeding problems

The techniques used for forming a wildcat from a parent case are fairly easy to perform.

• Cold forming. The parent case is well lubricated and forced carefully into the reloading die for the wildcat caliber. This will swage the case into the new shape. This type of operation is used for reducing case dimensions, such as reducing the neck diameter or pushing the shoulder back, or changing the neck diameter.
• Fire forming. This consists of taking the parent case, or a partially cold formed case, loading it with a light bullet and light load of powder, and firing it in the firearm it will be used in. Another technique uses a charge of fast burning powder topped with a case full of Cream of Wheat and a wad, to form a special blank cartridge that will expand the case. This technique is used for increasing case dimensions, such as pushing the neck forward, increasing the neck angle, or straightening the case walls.⁴
• Trim to length. Generally, after either a cold forming or a fire forming operation, the mouth of the case will be longer than ideal, and the case will be trimmed back to the "trim to" length. Trimming is a normal reloading operation, as high pressure cartridges will flow each time they are fired, and periodically need trimming to remove the brass that flows to the mouth.

Some of the case reforming operations used to develop a wildcat are:

• Changing the bullet diameter. Called "necking up" or "necking down", this is the most common way of making a wildcat. The new caliber allows a much different range of bullet weights, and can greatly increase the velocity or the power compared to the parent cartridge.
• Necking back. This is a cold forming operation where the neck is pushed back to reduce case capacity. This is often done when developing rounds for shorter barrels, such as turning a rifle cartridge into a handgun cartridge.
• Blowing out. This is a fire forming operation that moves the shoulder forward to increase case capacity.
• Changing the shoulder angle. By making the shoulder closer to square, the resulting space is closer to the ideal spherical shape, resulting in a more efficient burn. If the shoulder is also to be moved back, this is a cold forming operation; if the shoulder is to stay or be moved forward, it is a hot forming operation.
• Reducing the case taper. This makes the cartridge more cylindrical, giving similar results to a shoulder angle change. This is always a hot forming operation.
• Changing the rim. While this is a wildcatting operation, it is generally only done by commercial operations, due to the precision turning needed. Generally this is a conversion from rimmed to rimless cartridge, or from rimless to rebated, and is done to allow a larger parent case than the firearm action was designed for. The opposite operation, adding a rim to a case, is also generally only done by major manufacturers; examples are the .45 Auto Rim, a rimmed .45 ACP allowing ejection in .45 revolvers without the use of moon clips, and the .307 Winchester, a rimmed .308 Winchester, developed for use in lever-action rifles. A handloader can add a rim, by swaging a ring of metal onto a rimless case, then turning it down, but this is very labor intensive process and requires a special swaging die and precision metalworking lathe.⁵ It is far easier for most handloaders to simply start with a rimmed case, either of the desired diameter or reamed out as desired.
• Increasing the case length. This is commonly done by major manufacturers to make magnum cartridges, such as the .357 Magnum from the .38 Special, and is usually involves making the case from scratch. However, it is possible to draw an existing case into a slightly longer form, thinning and stretching the existing case, but this is an operation requiring special equipment and expertise.⁵ Again, it is far easier to start with a longer case and trim it to length.

Example wildcat cartridges

.243 Winchester Ackley Improved (left) and .243 Winchester (right)

There are more wildcat cartridges than there are production cartridges, though most wildcats are only used by a few shooters. This is a list of some representative wildcats.

• .30 Herrett. Based on the .30-30 Winchester, necked back and with a sharper shoulder angle. Developed for use in pistols with barrels as short as 10 inches (25 cm), it develops the same power as a .30-30 with greater efficiency and less muzzle blast.⁶⁷
• .357 Herrett. Like the earlier .30 Herrett, this cartridge is based on the .30-30 Winchester, shortened and necked up to .357 (9 mm). Designed for use in short barrels, the resulting cartridge is more efficient and more powerful than the .30-30. Often considered one of the best medium game hunting calibers available in the 10" (25cm) barrelled Thompson Center Arms Contender pistol.⁸⁷
• .10 Eichelberger Long Rifle. This is one of a smaller number of wildcats based on rimfire cartridges. It is made by disassembling a .22 Long Rifle cartridge, and re-using the case. The .10 caliber (2.5 mm) is the smallest rifled barrel made. The tiny .10 caliber bullets produce almost no recoil and travel at very high velocities. While it can be used on small game at short ranges, this cartridge is more of a curiosity than a practical hunting or target round.⁹
• 5.7 MMJ, or 5.7mm Spitfire. A .30 Carbine case necked down to .223 caliber (5.56 mm), this cartridge was developed to convert military surplus M1 Carbines into short range varmint guns.⁷
• 6 mm PPC. Based on the .220 Russian, which is in turn based on the 7.62 x 39 mm assault rifle cartridge. The 6 mm PPC was developed in 1975 specifically for benchrest shooting. While it is anything but common anywhere else, the 6 mm PPC unseated the .222 Remington from its 20 year spot as the best benchrest cartridge available. Chambered only in single-shot rifles due to its short, fat case and sharp shoulder angle, the 6 mm PPC is still going strong in benchrest after 30 years.
• .22 Eargesplitten Loudenboomer. This humorously named cartridge was developed by P. O. Ackley specifically to exceed 5,000 ft/s (1,500 m/s) muzzle velocity. Based on a .378 Weatherby Magnum case, the case is impractically overpowered for the bore diameter, and so the cartridge remains a curiosity.¹⁰¹¹

Commercially accepted wildcats

Some cartridges start out as wildcats, and gain wide enough acceptance to become commercial cartridges.

• .22-250. Based on a .250 Savage case, the .22-250 is still one of the fastest shooting .22 caliber (5.56 mm) cartridges available. First offered in a factory firearm by Browning in 1963 (the first factory gun chambered for a wildcat), the .22-250 was later adopted by Remington as the .22-250 Remington.¹²¹³
• 7 mm-08. A .308 Winchester necked down to 7 mm (.284 caliber), the 7 mm-08 provides a flatter trajectory with lighter, more aerodynamic 7 mm bullets. It provides nearly the performance of a 7 mm Magnum, but can use a shorter rifle action and does not need a belted case.¹³
• 7-30 Waters. Designed to improve the performance of lever-action rifle designs dating back to the 1890s, the 7-30 Waters is a .30-30 Winchester necked down to 7 mm (.284 caliber). Even with the lower chamber pressures allowed by the lever-action rifle and the flat tipped bullets necessitated by the tubular magazines, the 7-30 Waters offers a significant gain in velocity and sectional density with little loss in bullet weight. This cartridge has also developed a following among handgun hunters using single-shots such as the T/C Contender or G2, which can take advantage of spitzer (pointed) bullets that are unsafe in tubular magazines. Very efficient on small to medium sized game including whitetails and mule deer.¹³
• 6.8 mm SPC. This cartridge was developed by American military special operations soldiers in search of a more lethal round than the 5.56 x 45 mm NATO. It is based on the .30 Remington cartridge necked down to .270 caliber, and sized to fit in the M16 rifle. The 6.8 SPC is currently deemed unlikely for official military adoption, but is fielded by special operations troops in Afghanistan and Iraq and is gaining popularity as a commercial round.¹³
• .454 Casull. This revolver cartridge, a lengthened .45 Colt, was developed by Dick Casull and Jack Fulmer in 1957 as a high-powered big game hunting round. For many years, the small Wyoming manufacturer Freedom Arms was the only substantial maker of guns for the cartridge. In the mid-1990s, two major manufacturers, Ruger and Taurus, started selling guns chambered in .454 Casull. It was finally commercialized in 1998, when SAAMI published its first standards for the cartridge.¹⁴¹⁵
• .25/.303. A .303 British cartridge necked down to fire a .25 calibre projectile, developed in Australia during the 1940s as a Kangaroo culling and pest control round. Popularised in the late 1940s and 1950s in New South Wales, owing to restrictions in that state on ownership of .303 British calibre firearm and the difficulties of obtaining commercial hunting arms and ammunition from overseas. Now largely obsolete, but there are still large numbers of converted Lee-Enfield rifles chambered for this round in Australia.⁷

Commercially developed wildcats

Some cartridges go through a "wildcatting" process by firearms or ammunition makers. It is easier to start with an existing case in the early stages of development, and commonalities in the parent cartridge often make building firearms chambered for the new round as simple as making a new barrel. While these rounds never exist as true "wildcats", the goals and development process are much the same.

One of the features that is possible with a commercially developed wildcat that is much harder with shooter developed wildcats is the ability to add length a case to add capacity, or prevent case capacity loss when necking down. One example of such a cartridge is the .222 Remington Magnum, which is a stretched .222 Remington. It is not possible to construct a .222 Rem. Mag. from the .222 Rem. case, so this is arguably not a wildcatting operation, but the resulting cartridge can take advantage of existing components since the other cartridge case dimensions (most importantly the case head and rim size) are the same.

• .38-40. One of the oldest wildcats, the .38-40, introduced in 1873, was made by necking down a .44-40. Actually a .401 in (10.2mm)¹⁶ cartridge, the .38-40 had faded into obsolescence before being revived with the growing popularity of Cowboy action shooting. The ballistics of the .38-40 are close to the those of the .40 S&W.¹⁷
• .221 Fireball. This cartridge was developed by Remington for the XP-100 pistol, which was a single shot bolt action pistol. The .221 Fireball was a necked back .222 Remington, designed for greater efficiency in the 10 in (25 cm) barrel of the XP-100. Even loaded with a smaller load of faster powder for the short barrel, the .221 Fireball lived up to its name, with a massive muzzle flash; the performance, however, was unheard of for its day: over 2700 feet per second (885 m/s) out of the short XP-100 barrel. It remains the fastest SAAMI approved handgun cartridge, and the cartridge is so efficient and accurate that it has been chambered in rifles as well.
• .22 Remington Jet. This cartridge was developed by Remington for a Smith & Wesson Model 53 revolver and a Marlin Model 62 lever action rifle, but the rifle was never produced in this calibre. The .22 Remington Jet was a shortened .22 Hornet.¹⁸ The .22 Jet is no longer manufactured by Remington or other commercial manufacturers.
• .357 SIG. This cartridge was developed to produce ballistics to match the 125 grain (8.1 gram) .357 Magnum revolver load in a semi-automatic pistol cartridge. The cartridge was made by necking down and slightly stretching the .40 S&W case, which itself derived from the 10 mm Auto.
• .400 Corbon. This cartridge was designed produce 10 mm Auto ballistics in a cartridge that could be chambered in a .45 ACP pistol with a simple barrel swap. It was made by necking a .45 ACP down to .40 (10 mm). Initially, no firearms were available in .400 Cor-Bon, but barrels in the new caliber were produced for the M1911 pistol.
• .41 Action Express. This was a more involved wildcat produced for the Jericho 941 pistol. It started with a .41 Magnum case, cut down to fit in a semi-automatic pistol chambered for 9 x 19 mm. The rim was then turned down to the same dimensions as the 9 x 19 mm, making it a rebated rim cartridge. This allowed a unique switch up to a larger caliber. The .41 AE was a promising cartridge, which was rendered obsolete by the introduction of the better backed .40 S&W.¹⁹
• .204 Ruger. Introduced in 2004, this currently holds the title of fastest production cartridge, with a velocity of 4225 ft/s (1290 m/s) with a 32-grain (2.1 g), .204 bullet from a 24-inch (610 mm) barrel. Intended as a varmint rifle cartridge, the .204 was based on the .222 Remington Magnum, which is slightly longer than the .223 Remington and offers about 5% more case capacity. Designed to have a very long point blank range, the factory loading offers impressive ballistics, 1.5 inches high at 150 yards (140 m), and 1.5 inches (38 mm) low at 277 yards (253 m).

Second (and later) generation wildcats

Some wildcats are based not on commercial rounds, but on other successful wildcats. The .308 x 1.5" Barnes, a wildcat from noted cartridge author Frank Barnes made by simply necking a .308 Winchester back to 1.5 inches (38 mm) in length (38.1 mm) is probably the best example of a wildcat that has spawned many other successful wildcats. The .308 x 1.5" case is available from a number of case manufacturers, and differs from a homemade .308 x 1.5" in that it has a small primer pocket, where the original .308 Winchester case has a larger primer pocket (the smaller primer is more suited to the smaller case capacity of the short round). There are at least 8 wildcats that are made from the small primer .308 x 1.5" brass, including some very successful benchrest rounds, including the Benchrest Remington family of cartridges, .22 BR, 6 mm BR, 6.5 mm BR, 7 mm BR, .30 BR.

Another example is the .220 Russian, based on the 7.62 x 39 mm. Since nearly all 7.62 x 39 mm ammunition made in the 1970s used the complex to reload Berdan priming, and often steel cases, it made a poor choice for wildcatting. The .220 Russian, however, was and still is readily available in Boxer primed, brass cases of high quality. The .220 Russian is still the parent cartridge of choice for the PPC line of cartridges, such as the .22 PPC and 6 mm PPC, even though there are far more PPC chambered firearms avaialable than .220 Russian chamberings. Likewise, the PPC line of cartridges were the parent case of the 6.5 Grendel, a long-range, high-energy cartridge for the AR-15 platform.²⁰

Evolution into a production cartridge

Wildcats that become popular can turn into commercial cartridges. The .22-250, for example, started out as a wildcat consisting of a .250 Savage cartridge necked down to accept a .22 caliber (5.56 mm) bullet, and it is now a commercial cartridge offered by many ammunition makers, with many production firearms chambered for it.²¹

Generally the first step in a wildcat becoming a commercial cartridge is a commercial firearms maker offering the chambering. Once popular enough, funding is generated for SAAMI standards development. Once SAAMI standards are in place, any firearms or ammunition maker can be sure that any products manufactured to the SAAMI standards can be safely used.

Australian wildcats

Australian wildcats are a unique breed. Made primarily for hunting kangaroo, they are generally based on the .303 British, using surplus military actions rebarreled to around .22 to .25 caliber (5.5 to 6 mm), with the .222 Remington and variants also being popular in commercial actions. One of the unique features is that these cartridges relied less on the individual shooter handloading, but were often offered as proprietary cartridges from gunsmiths. Since having an existing barrel rebored and rechambered is less expensive than buying a new barrel, a .22 caliber with a shot-out bore could be rebored and rechambered to .228, then .25, then 6 mm. Also popular were the "Tini-Mite" and "Mini-Mite" cartridges, .17 caliber cartridges based on the .22 Long Rifle case.¹

See also

• Thompson/Center Ugalde family of wildcat cartridges
• P.O. Ackley's wildcats, including the common Ackley Improved versions
• Whisper Family of Firearm Cartridges, proprietary cartridges by J. D. Jones
• Wildcats for Special Applications

References

External links

• The Wild Cat: An Endangered Species? Guns Magazine, Dec, 2000 by Charles E. Petty
• Loading Wildcat Cartridges: a Few Simple Considerations Make Life Much Easier Guns Magazine, August, 2005 by Charles E. Petty
• Wildcat Cartridges wildcat cartridge descriptions at The Reload Bench
• Reloading Techniques: .22 Win. Magnum Rimfire, Performance Shooter, April 1996