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My Wildcat Cartridge

By
Scott Mayer
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Scott’s .400 Marlin wildcat duplicates the ballistics of the old .405 Winchester that Teddy Roosevelt used for rhinoceros.

A “wildcat” cartridge is one where a hobbyist shooter comes up with on his or her own unique cartridge usually by necking an existing one up or down to a different caliber. Some get “legitimized” when it proves so popular that a manufacturer puts it into production, such as the .257 Roberts, which is the 7x57mm Mauser necked down to .25-caliber, but most remain proprietary.

You can see how this bullet performed on a big Montana whitetail in Realtree’s “Monster Bucks 11” video.
You can see how this bullet performed on a big Montana whitetail in Realtree’s “Monster Bucks 11” video.

There is probably nothing you can wildcat today that hasn’t already been done, so when Hornady and Marlin teamed up to create the .450 Marlin with an all-new, never-before-seen case, I saw my opportunity to do what no one else had done and wildcat it.

The longest shot Scott has taken with the .400 Marlin is 211 yards using the 235-grain Hawk bullet. The deer dropped in its tracks.
The longest shot Scott has taken with the .400 Marlin is 211 yards using the 235-grain Hawk bullet. The deer dropped in its tracks.

At the time,.45-caliber in-line muzzleloaders were starting to gain popularity. They’re ballistically superior to .50-caliber for deer and since they used saboted .40-caliber bullets, I reasoned that there would soon be a bunch of quality .400-inch rifle bullets on the market and made the “.400 Marlin” a true .40-caliber instead of the more commonly available .416-inch.

This 200-grain .400-inch Hornady XTP Mag bullet took a caribou at 44 yards. What little remained of the bullet was found inside the off-shoulder.
This 200-grain .400-inch Hornady XTP Mag bullet took a caribou at 44 yards. What little remained of the bullet was found inside the off-shoulder.

The resulting .400 Marlin did what I wanted it to do—basically duplicate the old .405 Winchester like Teddy Roosevelt took his black rhino with, but in a gun with an 18 1/2-inch barrel. Unfortunately, popularity of .45-caliber in-line muzzleloaders soon fizzled and an abundance of good bullets never materialized.

Though designed as a pistol bullet, Scott’s notes show this Hornady XTP Mag broke both shoulders of a bull caribou when fired from his .400 Marlin wildcat.
Though designed as a pistol bullet, Scott’s notes show this Hornady XTP Mag broke both shoulders of a bull caribou when fired from his .400 Marlin wildcat.

I’ve taken a couple of caribou using the .400 Marlin loaded with 180-grain Hornady XTP Mag pistol bullets intended for the 10mm Auto, and Hawk made up some 235- and 300-grain roundnose bullets that I also use. If you ever get a chance to watch Realtree’s “Monster Bucks 11” video, you can see the 235-grainer poleax a big Montana whitetail at 211 yards.

Scott’s .400 Marlin wildcat duplicates the ballistics of the old .405 Winchester that Teddy Roosevelt used for rhinoceros.
Scott’s .400 Marlin wildcat duplicates the ballistics of the old .405 Winchester that Teddy Roosevelt used for rhinoceros.

Clearly I’ll never take a rhino with the .400 Marlin, not just because of bullets, but I can’t afford a rhino! But my .400 will always be a fun, big-bore, close-range gun for deer, bear or elk. I’d say it’s “unique,” but even though I used the then-new .450 Marlin case, it turns out that decades earlier O.A. Winters had wildcatted the .458 Win. Mag. into essentially what I had created.

 

 

Scott Mayer

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Scott Mayer
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