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.
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.
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.
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.
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.
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.
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