It’s All About the Wildcat Cartridge

.22 Eargesplitten Loudenboomer case head

I thought a good topic to discuss would be one that we don’t hear about much these days and that is wildcat cartridges. The term wildcat cartridge is used to describe a custom-made cartridge, most often inspired, and made by modifying an existing commercial cartridge. It is usually developed by individuals to optimize a given cartridge’s performance to obtain more power, more velocity, flatter trajectory, or better accuracy, etc.

Because they are custom-made, they are not available the way commercial cartridges are. Because of the limited market for them, commercial cartridge manufacturers generally don’t manufacture them until they generate a large enough following. Wildcat cartridges are most often deep in the domain of very serious shooters or handloaders.

The illustration shows a .243 Winchester Ackley Improved wildcat cartridge on the right compared to a normal .243 Winchester cartridge on the left.
The illustration shows a .243 Winchester Ackley Improved wildcat cartridge on the right compared to a normal .243 Winchester cartridge on the left.

Specific Needs

Because individuals create the need for a wildcat cartridge, there are more varieties of Wildcat cartridges than commercial production cartridges. Most wildcats are produced in very small quantities compared to their commercial counterparts. In some cases, cartridges start out as custom-made Wildcat cartridges, because the originator wants to solve a specific ballistic challenge. Sometimes, his efforts gain enough popularity that they become commercialized, and rifles chambered for them become available commercially with SAAMI standards specified for them.

A famous example of successful cartridge experimentation involving an existing cartridge is that of the .357 Magnum, which was originally developed from the .38 Special cartridge. Early versions of .357 Magnum were identical in size to .38 Special cartridges. The .357 and .38 Special cartridges are both the same diameter externally and only differ slightly in length because of safety reasons. The length was increased slightly so that you could not accidentally load the more powerful .357 Magnum cartridges into a firearm not designed for the additional pressure.

Another example of what a wildcat would be is the 6.8mm SPC, which was originally developed in collaboration with members of U.S. SOCOM. The 6.8mm SPC is based on a .30 Remington cartridge. It was then modified to .270 caliber and then further modified in length to fit in magazines that can fit the magazine wells of the M16 rifle.

Any M16 or AR15-type rifle only needs to replace the barrel, bolt, and magazine to use this new cartridge. This cartridge is more effective than the standard NATO 5.56x45mm cartridge fired by the M16. Though it has not been officially adopted by the military, it has found use by special forces troops in Afghanistan and Iraq, and is gaining popularity as a commercial civilian round.

Pocket Manual for Shooters and Reloaders
P.O. Ackley’s definitive manual on his modifications and Wildcatting.

Another example of a very successful cartridge that started as a Wildcat is the 6mm PPC (Palmisano & Pindel Cartridge, named after its inventors, Lou Palmisano and Ferris Pindell). That cartridge started out as an improvement of the .220 Russian cartridge, which was itself based on the 7.62x39mm cartridge used in the AK-47 and AKM rifles.

The 6mm PPC case is made by forming the .220 Russian brass case into a new shape and is specifically geared for single-shot benchrest shooting. It became one of the most accurate cartridges available out to 300 yards and has been produced commercially since 1975. Its design concept validated the short wider powder column concept for accuracy.

Barrel Modification

As stated previously, wildcat cartridges are generally used by serious shooters. This is because wildcat cartridges often require barrel modifications to be used. The modified barrels are usually supplied by custom barrel makers, who typically work out of small shops.

P.O. Ackley at work in his shop.
P.O. Ackley at work in his shop.

Custom barrel makers will also supply the buyer with reloading tools and dies, so the buyers can make their own cartridges. Some barrel makers also supply data about how different powder brands, quantities, and bullet weights perform with their barrels. Many wildcat cartridges have been developed by custom barrel makers or by someone who is working in conjunction with a custom barrel maker.

A wildcatter usually starts out using a commercial cartridge case they think can be improved by changing its shape to new dimensions. Usually, this involves pushing the shoulder of the cartridge backward or forward as needed to modify the case capacity. The wildcatter will also change the diameter and length of the cartridge neck. This process can be done by either cold forming (i.e., the case is pushed into a die and pressure is applied to change the shape of the case) or fire forming (i.e., the case is placed in a chamber of a different dimension and loaded with a light gunpowder charge. Upon firing the charge, the case takes the shape of the new chamber).

Sometimes a mixture of both methods is used to make the final case shape of a wildcat cartridge. Next, the wildcatter trims the case to the appropriate length, because cold forming or fire forming generally tends to increase the length of the case’s mouth and the excess length needs to be trimmed. Then the diameter of the neck is changed as needed for the new bullet. The cartridge is then hand-loaded carefully and a bullet is seated.

.22 Eargesplitten Loudenboomer right, compared to a smaller cartridge
It was originally a .50 Caliber BMG cartridge as seen in the photo. It was more practically rebuilt on a .378 Weatherby Magnum case, intended solely to exceed 5,000 ft/s muzzle velocity. Ackley’s loads only managed 4,600 ft/s (Mach 4.2), firing a 50-grain bullet. It is impractically over-bore for the bullet diameter, and so the cartridge remains a curiosity.

One of the most famous wildcatters of all time was P.O. Ackley. He was credited with the modifications known as the Ackley Improved Series of cartridges. In this series, he reduced the taper of the case and the angle of the shoulder which increased the propellant capacity of the case, ergo increasing its performance.

The entire family of Ackley Improved Cartridges was developed by Patrick Otto Ackley. Ackley was also a prolific gunsmith and author. He produced many improved versions of commercial cartridges in various calibers.

When I was young, dumb, and new to the firearms community, I used to go to Bob Hutton’s Rifle Ranch in Topanga Canyon California. Bob Hutton was the technical editor of Guns & Ammo magazine from 1959 to 1974 and a very respected ballistics expert. On one shooting trip, I was fortunate enough to meet Mr. Ackley while he was visiting Bob and doing some testing. Back in the day, Southern California was where everything shooting was happening.

Most firearms can be easily modified to use the Ackley Improved Series of cartridges. For example, the .243 Ackley Improved cartridge shown above could easily be used by rechambering an existing .243 Winchester firearm. An advantage of all “Ackley Improved” firearms is they can also fire standard, factory-loaded ammunition. This allows the owner to use commonly available ammunition, should he or she run out of wildcat cartridges.

Another interesting wildcat that became a commercial success was the .458 Lott. For those of you not familiar with Jack Lott, he was a big game hunter and writer. I had occasion to be seated with Jack Lott at a Professional Hunters dinner prior to the introduction of the .458 Lott Cartridge. Lott told of its genesis, and his adventures in the bush war of Mozambique, in a very interesting fashion.

In 1959, Jack had an adverse encounter in Mozambique with a Cape buffalo, in which he was injured. He had been hunting with the then-new .458 Winchester Magnum. That experience convinced him that a more powerful cartridge than the .458 Winchester Magnum was required for hunting dangerous game. After the encounter, he began a search for a big bore cartridge that would suit his needs more perfectly.

Bob Hutton working a metal lathe with a gun barrel inserted
In addition to being an editor for G&A, Bob Hutton owned and operated the Hutton Rifle Ranch in Topanga, California — a shooting and firearms testing and training center.

The .458 Winchester Magnum that almost got Jack killed was put into production in 1956 and was an immediate commercial success. At the time it was a more economical alternative to the English double rifles that were considered the standard for dangerous game hunting in Africa. The .458 Winchester Magnum promised to emulate the performance of the .450 Nitro Express in a cartridge designed to fit a standard-length bolt-action rifle.

From reports coming in from the field, it soon became apparent that the .458 Winchester Magnum was not performing as anticipated. Several factors contributed to its less-than-stellar performance in Africa. The most notable problem being it never generated the power required to be effective. Jack’s search did not find a cartridge that would fill his needs, so he set out to design a cartridge to fulfill his needs in a dangerous game cartridge.

Jack Lott’s original concept drawings of the cartridge were done on a napkin during a diner engagement. It was based on the full-length .375 H&H Magnum blown out and shortened to 2.800 inches. The first cases for the new rifle cartridge were fireformed from .375 H&H Magnum brass in a .458 caliber chamber. The .458 bullets had their bases resized to .375-inch, so they would fit in the mouth of the .375 H&H Magnum case. This method of fire forming left the newly formed cases slightly shorter than the parent cases. The resulting cartridge was named the .458 Lott in Jack’s honor.

.458 Winchester Magnum ammunition
The illustration shows the .458 Winchester Magnum cartridge on the left, compared to the .458 Lott cartridge on the right. The illustration shows the .458 Winchester Magnum cartridge on the left, compared to the .458 Lott cartridge on the right.

While the cartridge was slow to gain popularity at first, Jack’s effort became the standard by which dangerous game cartridges are now judged. As intended, the cartridge provides a distinct step up in performance over the .458 Winchester Magnum. As a side note in honor of our friendship, I had a custom rifle built and chambered in .458 Lott.

I hope this helps clear up any misconceptions you may have had concerning Wildcat Cartridges and perhaps inspires you to create the next great do-everything Eargesplitten Loudenboomer. Stay Safe!

Do you have a favorite wildcat cartridge? Share it in the comment section.

  • .22 Eargesplitten Loudenboomer case head
  • Custom bolt-action rifle chambered in .458 Lott
  • Pocket Manual for Shooters and Reloaders
  • .458 Winchester Magnum ammunition
  • The illustration shows a .243 Winchester Ackley Improved wildcat cartridge on the right compared to a normal .243 Winchester cartridge on the left.
  • Jack Lott at the bench regulating a double rifle.
  • Bob Hutton working a metal lathe with a gun barrel inserted
  • .22 Eargesplitten Loudenboomer right, compared to a smaller cartridge
  • P.O. Ackley at work in his shop.
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Comments (18)

  1. You would think that someone would fact check this article before posting. A couple of errors are found here 1) the 6.8 spc is a saami approved commercial round developed by Remington and the US Army marksmanship unit between 2002 and 2004
    2) the 6mm PPC is not and never has been saami approved commercial cartridge.
    there’s plenty of information out there on both these cartridges from multiple sources to confirm this so it makes me wonder what else in the article is just the author blowing hot air. I am very disappointed in this article.

  2. @GDB

    Scroll down a bit and you will find my very similar story. But in the case of my wild cat I went with a highly modified 300 Winchester magnum case and as such I’m able to push 127 grain barns bullets at 3750 ft./s.

    So far on mule deer and elk it is performed marvelously

  3. Came to admire the 22WMR and started adding pistols and rifles to my collection. Then when the elections happened that put Obama in the White House, my little favorite varmint cartridge was nearly impossible to find. Started scheming and then designing and produced my own varmint cartridge to fill that void, putting me more in control of supply. I designed what my friend called the 223 RMAC from a 9MM case and using 40 gr .224 bullets. Going against the hundreds of nay-sayer’s I had a Savage Axis .223 rifle rebarreled in my chamber and proved my cartridge on ground squirrels out to 150 yds. Max velocity came out over 3000 fps but 2770 is my accuracy zone. Doing a bolt action AR side charging design for this now because the little pill is really too short for front lug bolt guns and 9MM ARs are easy to build. Yes, you need to stock up on powder, primers and bullets but I covered that back when I saw the social/political writing on the wall. Going to add another video to my YouTube channel when I get this build completed. I still have plenty of 22Magnum on hand for quick trips out to the desert.

  4. Great article. Hope to see a lot more like this one. Mr. Ackley Mr. Lott Mr. Weatherby and all the others too numerous to mention have given us some absolutely great cartridges. I know there are hundreds if not thousands of Wildcats that have been constructed over 125+ years but my favorite will always be the 25-06.

  5. I like Liberty’s +P 45ACP & .357M They are 78gr & 50gr & go 1900fps & 2100fps.
    Pilgrim also has them. They use solid Nickel HPs. They’re costly yet have a 700yd range.

  6. Back in 1990 I had a less than perfect experience with a Ruger M77 in 280 Rem, missing (low) an 8-pt some 400 yards distant. As a result, I was determined to come up with a flat shooting cartridge that would perform well at these type distances. What i came up with was a 6.5x.257 Roberts AI (Douglas) on a Ruger M77. I found it was capable of sending a 129gr Hornady bullet downrange at 3200 fps. i have taken it out to Colorado multiple times, and it has not let me down. That 129gr at 2975 fps drops ’em right there.

  7. I built a 22-250 AI from a Yugo mauser, and posted my story, and pics, on, and for the longest time when you googled ’22-250 AI’ my pic would be the first to show up. Things have changed; now many people have their pics out there too.
    I love my 250; I moved to SD and now can find 1000 meter ranges to try my long range skills.

    Funny how the PO Ackley picture above said “. . . to exceed 5000 fps”; my 250 can do that [not with a 50 gr bullet, but with a 40]. I don’t go that high; i’m happy with a 50 gr bullet at 3700.

  8. I am surprised that no one has brought up the marketing genius and patron saint of us speed freaks aka velocity whores, Roy Weatherby. To a much lesser extent but still a player, Lazzeroni.

    I won’t allow a push feed bolt action rifle infect my gun safe, but I have loved and enjoyed using many of ol Roy’s cartridges built on good magnum Mauser and similar controlled round feed, fixed ejector, claw extractor actions.

    With todays excellent monometal bullets with thier long body and ogive have made the concept of light for caliber/mega speed cartridges. My newest wildcat pushes a mere 127gr Barnes LRX .264 diameter bullet but it leaves the barrel at 3,700fps. So far two rounds fired and two bangflop/DRT kills on a cow elk and a very large 4×4 mule deer but.

  9. Just went to DuckDuckGo. Checked “K Hornet” and “Mashburn Bee” – both 22 caliber wildcats. Any number of sites for them. Used both of them back in the 1960’s, built on small Martini actions. Great cartridges for dingoes. Ballistics just short of the 222 Remington.

    At the same time the 303/25 had been standardized, but the 303/22 came in three different versions – three different case lengths. Memories…..

  10. Super interesting article. Growing up in Southern California I had heard of Bob Hutton but never met him. It was great to see his photograph along with that of PO Ackley. Those two guys along with Jack Lott were nothing short of genius…..the “wheels” of their minds never stopped turning!

  11. Very informative article lots of good info most would not know about, keep them coming Ed looking forward to the next one!

  12. I have always wanted a 280 Ackley Improved, as I have always been a fan of the 7mm diameter cartridges. My very first rifle was a Remington model 700 in 7mm Rem Mag, and later on I added a 7mm-08.
    The reason I haven’t added the A.I. to my collection is solely because of the “time hassle.”
    Unfortunately, I have only limited time to mess with things before and during a hunt.
    I also suppose that the performance not giving any significant gains factors in as well.
    Without “wildcatters,” though, we would not have a lot of the great cartridges we do today, nor would manufacturers likely be inspired to make the innovations that they have…

  13. Very good article and topic! One of my favorites. I have had and still have a good number of rifles In AO cartridges, and have designed a few wildcats of my own including the 340 Tyrannosaur which duplicates the 338 Lapua but pre dates it and uses ordinary belted magnum cases and my newest one the .264 Claiborne Super which duplicates the 26 Nosler and 6.5/300WBY but functions and feeds perfectly in a standard length controlled round feed, blade extractor, fixed ejector action such as a ‘98 Mauser, commercial variants tjereof and pre 64 model 70 actions such as used on my custom build long range deer blaster.

  14. Great article, tons of new history for me. Gotta respect the innovation and boldness of these gentlemen. Thanks to the author!

  15. “Wildcatting” is almost as old as the metallic cartridge. However, with modern technology, it is much easier to “create” a new cartridge. With that said, many of the “wildcat” cartridges of yesterday are now SAAMI approved. Examples are like the 22-250, 257 Roberts, ,243, and numerous others. In today’s world, there are a number of vintage cartridges that are ideal candidates to be updated, using new powders and reshaping the cartridge case. Think if someone looked at the 5.7 JOHNSON SPITFIRE (necked down .30 Carbine to .22 caliber) and used that as the parent case for the 5.7×28 cartridge, what impact that would have had. That resulting small increase in powder capacity over the current 5.7×28 case is significant, performance wise. But, getting people interested in any new cartridge is a crap shoot.

  16. I have long been intrigued with the practice of “Wildcatting” new and different caliber cartridges for specific applications and even “Tinkered” with it myself.
    Some years back I came into possession of a J. Stevens 22 cal. Rifle Action with a short length of barrel and chamber still attached.
    My foray into creating a “Wildcat” Cartridge centered on “Necking Down” a Primed 22 Lr. Case to .177 dia. And seating a 17 cal. Lead Bullet that I had machined Swadging Dies to form.
    My intention was to create what I would call the 17 Long Rifle.
    Less power than the recent batch of 17 Rimfire Cartridges introduced and Way Cheaper to Feed but with an established market base desiring a Small Varmint and Pest Control application in mind.
    Sadly, my time at the Machine Shop was cut short by 9/11 and the Layoffs that followed.

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