Ideas for Wildcat Cartridges

For people who believe that wildcatting is dead.

   Thoughts about 'Improving'



      7mm Mauser Maximum                                       303 Newmag   



     The Bolt Action 405 Winchester                          7,62 Mosin Nagant Improved



   300 Magmax                                                          9.3x64 ‘cats



 7mmICM (Ideal Capacity Magnum)                      12x59



  9,3 Schauman Magnum


The MBM (Medium Beltless Magnum) Family:







WILDCATS are non standardized cartridges of private origin and therefore not commercially available. Some WILDCATS have become so popular over the years that chamber reamers and reloading tools are now stock items of several manufacturers. There are many reasons for designing and building a WILDCAT. To mention a few:


You have a rifle since many years and you like it very much but you don't shoot it very often because you consider the cartridge too weak or too strong. Rechambering or rebarreling can pump more life in this old iron.

Your favourite rifle has a worn barrel. Reboring and rechambering give it a second life.

You are thinking about a cartridge that can quite closely approach the performance level of a popular commercial round but with less expense.

You discover a gap on the market- whether it's real or not.

You are dreaming of a rimless counterpart to a famous rimmed or belted cartridge or vice versa.

You have a huge quantity of cases in one caliber and you are thinking about converting them to a more potent cartridge that will fit better to your specific needs.

You are seeking a way to get a very individual gun.

You just want to have more fun while shooting and reloading.


This list is nearly endless.


Sometimes 2 people have created a very similar wildcat at a different time not knowing of each other and therefore any design could already exist since many years bearing another name but having nearly the same dimensions. When you have an idea for a new cartridge you should always count that someone else had the same idea before.

That’s an impressive example:

Top: 338-270 HGT (probably first built in the 1970s)

Bottom: 8,5x63 (first built in the 1980s, designed by Werner Reb, NO wildcat, CIP-Standard since 1987)



That can happen to a case:

Since its introduction in 1936 the 348Winchester served as basic case for many designers. The main reason is probably the large potential volume relativ to its length. By reducing body taper and adding a short neck you can reach magnum performance in many calibers rather elegantly. Maybe there is no other rimmed case which was modified to rimless so many times. One could believe that more cases were used for other cartridges than in its original caliber.

The real number of 348Winchester  based wildcats is of course higher than pictured below but even these 14 designs illustrate quite well what can be done to a case.





Heavy Express Magnum & Heavy Express Short Action Magnum cartridges, various lengths, designed by Jim Busha using 348Win brass for development.





The main idea behind this cartridge is maximizing powder space of a standard case while keeping shoulder angle and neck length on the moderate side( s. Thoughts about 'Improving' ).

The 7x57Mauser is a typical candidate for improving due to its long neck, long shoulder and old fashioned body taper.

After fireforming you will have a cartridge which has about 9% more powder space than its parent case. 7mmMauserMaximum loads (after fireforming!) should be based on reduced 7x57AckleyImp. data for working up. It is always a good idea to be cautious while approaching maximum pressure.

Its actual performance depends on several factors. As performance is most of all a function of powder space it is slightly more powerfull than the 7x57AckleyImp. and comes close to the 280Rem /7mmExpr..



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The Bolt Action 405Winchester:


Some years ago -not believing that nobody had the idea of using the 240WeatherbyMagnum case for a ‘big bore’ tapered wildcat- I found a link to a cartridge called .411Ryan designed by Robert Ryan.

The 411Ryan has been successfully materialized.

We can learn that the best case for forming is the .400-.375NitroExpress(H&H) and not the 240WeatherbyMagnum with its peculiar Weatherby ogee shoulder(see picture below):



                        Two 411Ryan cases:

Left case: 63.5mm/2.5in long, head stamp ‘400-375 NITRO’

                   Right case: 67,5mm/2.66in long, head stamp ‘411 RYAN’


A belted case with a distinct shoulder makes not much sense though up to the 1980’s belts should indicate superior performance in any caliber and in many minds. Using belts for a non bottleneck case is the most reasonable way to enjoy the benefits of belts. If someone is interested in getting a 405/411 caliber bolt action rifle the 411Ryan should be the first choice.



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or 475 OKH short or 470 Capstick short





Why this cartridge? – Because there is no 12mm/.475” of this class.

At the first glance the venerable 458 WinMag is more than enough for shooting 500grs slugs from a bolt action rifle. Regarding the curved trajectory of the 458WinMag one could try to get more or less identical performance (near the muzzle) by using less sectional density inside the barrel and a reduced powder charge. One result of course is an even more curved trajectory which is less important for the intended range of large caliber cartridges. And what about having more fun with 600grs bullets?

Cases can be built by cutting 300WeatherbyMagnum brass right at the shoulder/body junction (s. Picture).


From left to right: 458WinMag, 12x59, 300WeatherbyMagnum



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7,62 Mosin Nagant Improved

(30°, 35°, 40°)

Some cartridges have many names. Here we have a famous example. It is also called 7,62x53R, 7,62x54R, 7,62x54, 7,62Russian, 7,62Nagant, 7,62MN, 7,62 Mosin Nagant and maybe some more. To avoid any confusion with other cartridges I recommend to use 7,62 Mosin Nagant.

This is only one way to improve that well designed caliber. There may be some other versions based on other data sources and using longer or shorter necks.

But before you decide to convert your rifle you should consider some points:

-Finish rifles have tighter groove and chamber dimensions. They work well with .308 bullets and could need a reamer with slightly reduced neck and freebore dimensions

-Russian rifles can have very large chambers. A reamer ground to cut a minimum chamber will not clean one of these chambers entirely.

As far as performance is concerned the 7,62MosinNagant is a 308Winchester equivalent at lower working pressures. Any improved version will be more powerfull but it will not be a 30-06Springfield!


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9,3 Schauman Magnum 

A 350RemMag based Wildcat not only for rechambered Mosin Nagant’s



As a result of Finland’s history Mosin Nagant rifles were widely used for military purposes in the past and are still in use for hunting and sport today. It is a natural process under these conditions that many attempts have been made to convert rifles and the old military round for sporting needs. When additionally the Finnish hunting law between 1934 and 1962 has prohibited calibres for moose hunting smaller than 8mm, a variety of modifications is no surprise.

The good old 7,62 Mosin Nagant cartridge has been necked down to 5,7mm, 6,3mm and 7mm and necked up to 8mm, .338, 9,3mm, .458 and maybe some more. Many of these rounds were commercially manufactured for some decades and some cases for them can still be bought.





Necking up a cartridge gives new life for an old shot out barrel and sometimes improved ballistics, too. At a certain time these conversions were often made by local gunsmiths in Finland. Reboring leads to thinner barrel walls but makes action alteration not necessary if diameter changes are not too radical so that feeding could be a problem. There are also some ex-military Winchester95 rifles in use which were also converted to 9,3x53R or 8,2x53R mainly because their original 7,62mm bore was shot out!

Sporterized Winchester 95 Military Rifles

Sporterized WIN95 &  Mosin Nagant Rifles

For improving a 9,3x53R Mosin Nagant rifle a case with more powder space is needed. ‘Improving’ the Mosin Nagant type case could be one way but a new basic case is a bigger step forward. When the first ideas for this cartridge came up the 350RemMag was not in mind. The magazine of the Mosin Nagant rifle dictates maximum cartridge length and so a case length similar to the 350RemMag is logical. Another point to consider when you are determined to change the case is bolt head and extractor. Surprisingly some Mosin Nagant bolts can handle the common belted case head without any problems but some bolt heads need a treatment like this private solution:


The original 350RemMag ‘suffers’ a little under its COL. In a Mosin Nagant type rifle heavier bullets can be seated so far out that the whole inside volume is usable for powder.­­­­­

There is a tendency in several countries to ban lead containing bullets for hunting. Lead free bullets of a certain weight are longer than the lead containing one. Regarding this development a larger COL has more future potential.

The 9,3 Schauman Magnum is an inside volume twin of the 9,3x62. That made of course load development rather simple. It is using the barrel lead of the 9,3x53R. Actual measurements have shown that loads for the 9,3x66 Sako are more appropriate due to the superior strength of the magnum case head.



This picture shows a Mosin Nagant barrel rechambered for the 9,3SchaumanMagnum with a 9,3x53R case placed inside. The increase in powder space is obvious.


If you like to know more about the 9,3 Schauman Magnum write to Caj Schauman.



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303 Newmag: Picking Up an Old Idea

In 1920 Kynoch introduced the 303Magnum (bottom). This cartridge was based on the case of the 276Enfield (top) which was intended to become the new British service round when the First World War broke out and it seemed to be more reasonable to abandon this plan.




The case of the 276Enfield is of very interesting design, because base diameter to body length ratio is rather large and appears quite ‘modern’. The main proportions are nearly identical to the standard belted magnums. It would have been an excellent basic case for a lot of potent cartridges. Since the 375Ruger (a rimless case with .532 base dia) is available we can observe that phenomenom.

The 303Magnum existed in a rimless and a semi rimmed version. It served mainly as target round and for trials with boat tail bullets for the military.


Read more:  303-magnum-rimless



It would be interesting to get some information about the rifles in that caliber, too.


If it would be still available wildcatters would have modified it in several ways. If you believe that it could make sense to pick up this cartridge with its fat .30 caliber and convert it to a modern shape you will only find the 8x68S case and –due to it’s actual (Check it!) base dimensions- the 375Ruger for case forming. The .30Newton would be closer to the rimless original but it’s a collector’s item, too.

A formed, trimmed, neck reamed and fireformed case has an inside volume -including neck- of 82grs. of water. When loaded to the same pressure it is as powerful as the 300WSM/300SAUM.



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300 Magmax

This cartridge is (not only) for owners of 300WinchesterMagnum rifles who are sick and tired of dealing with belted cases.

It is based on the huge Remington Ultra Magnum case and has the same case and overall length as the 300WinchesterMagnum. All dimensions were defined to make sure that the chamber reamer will clean the 300WinchesterMagnum chamber completely except for the neck diameter.




The result is a very short neck which is nearly as short as that of the 30Gibbs. One disadvantage of the original cartridge will of course remain: protruding bullet bases.

Rechambering to this caliber is more than moving from a belted case to a rimless. The whole operation ends in a powder space increase of whopping 10% or an inside volume -including neck- of 100grs of water. That’s the capacity of the 300WeatherbyMagnum but powder space reduction by the bullet in this case is more severe!




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Wildcatting the 9,3x64 Brenneke


One way not to invent the wheel again is searching for a little known basic case. That means more or less little known outside Europe. But even among those very few cases one can find some clever designed wildcats. The 9,3x64 Brenneke for instance has some friends all over the world who appreciate its performance but due to the intermediate head and base dimensions only few manufacturer are currently chambering it. The introduction of the 376Steyr which uses a shortened 9,3x64 Brenneke case has not changed the situation substantially.


Some cartridges based on the 9,3x64 Brenneke:

8x64 Mazón / 8 mm Mazón / 8-9,3x64S Brenneke-Mazón (.323cal. , designed by Alvaro Mazón)


8,5x64 (.338 cal. , designed by Lutz Möller )


6,5x63 Messner Magnum (NO wildcat, CIP-Standard): 

These 9,3x64 Brenneke descendants are all one needs to imagine his own wildcat mainly by varying bullet diameters. If not, send an e-mail.

Small variations of shoulder angles and/or neck lengths will not affect performance very much.

Shooting a wildcat may be eccentric but shooting a 9,3x64 Brenneke wildcat really is eccentric!


                                       30 Hembrook Long

This is one of the rare 9,3x64 Brenneke wildcats, designed by Robert C. Hembrook.

The genesis of this cartridge started with the ownership of a rifle in 9,3x62 caliber and the meditation about other 9,3mm’s and the Brenneke case. After a 9,3x64 Brenneke case was placed near a 30-06Springfield the idea was born to use the larger volume of the 9,3x64 Brenneke for a .30 caliber cartridge of the same length- and obviously the same appearance.

It has slightly more inside volume than the 300WSM and therefore roughly the same performance when loaded to same pressures. Dimensions allow rechambering of any 30-06Springfield rifle and of course simple rebarreling of any 9,3x64 Brenneke rifle. As it is intended for standard length actions magazines can rather easily be adapted to this round. 30-06Springfield bolt heads must be opened up to this ‘special’ diameter, too.

If you like to know more about the 30 Hembrook Long write to Robert C. Hembrook.





                              7mm ICM (Ideal Capacity Magnum)

One can discuss a lot about the relationship between calibre and powder space volume. The 7mmWSM with its 82grs of water inside volume is very efficient with most bullet weights. The popular 7mmRemingtonMagnum has about 86grs and the huge 7mmSTW 97grs. Usually cases with larger powder space volume show their full potential clearly when it comes to heavier bullets. As it is so popular most shooters would agree that a 7mmRemingtonMagnum class cartridge is the best compromise among the hotter sevens.

The 7mm ICM is based on the shortened RUM case and is a shorter and fatter rimless 7mmRemingtonMagnum, also tailored for standard length actions. Ballistics are similar or slightly superior especially with long (heavy) bullets. Up to its maximum overall length there is much much space for long long bullets.

This design concept is not unique. The new 7mmBlaserMagnum manufactured by NORMA is a similar conclusion using a case with slightly different dimensions. Not to mention the 7mmExpress or 7mmWadeSuper (s. 348Win descendants).




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The MBM (Medium Beltless Magnum) Family

Combining ‘medium’, ‘beltless’ and ‘magnum’ in one name sounds a little strange but it’s the most precise description for the idea behind it. The COL(84mm or 3.31in) of all calibers makes it ideal for medium length rifle actions and performance is right between the short and the long action magnums. Most of them have a DAKOTA and a standard belted (hence ‘beltless’) counter part. As the DAKOTA proprietary cartridges are with us for many years this concept is anything but new. The whole family is based on the rather cheap Remington Ultra Magnum case instead of the more expensive 404Jeffery - the parent case of the DAKOTAs. All cases are 62mm (2.44 in) long and crowned by a sensational new shoulder angle of 32.5 degree.

They cannot be used for rechambering standard magnums. These cartridges provide performance of factory loaded belted or proprietary rimless magnums in a cheaper and (nearly) rimless case!


Water capacity including neck: 309 MBM: 94grs, 8mm MBM: 95grs, 338 MBM: 96grs.



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         Heiner Demenus