The .375-CCC and Other Obscure Cartridges
March 18, 2019
Any time you start handloading for an obscure round—especially a wildcat—the process is challenging. But when the outcome is finding a load that a special rifle shoots well, it’s definitely worth the effort. Case in point: the .375-CCC.
The .375-CCC is a big-bore belted magnum wildcat cartridge that first appeared sometime in the 1940s. It is very similar to the .375 Weatherby Magnum.
What little information I discovered while researching the history of this wildcat is interesting. Two fellows (E. Baden Powell and R.W. Miller) came up with the idea for a series of “improved performance” cartridges in the early 1940s.
They would accomplish this by rechambering an existing rifle to accommodate an oversized case. They set up a company, and the PMVF (Powell-Miller Venturi Freebore) concept was in business. Roy Weatherby ordered a .270 PMVF based on the .300 H&H Magnum case, and he was so impressed he later asked Miller to assist in developing a new line of “magnum” cartridges to be used in custom-ordered rifles.
In the meantime, the original company sold out to another outfit. That company offered the same service but gave the concept a different label—the CCC (Controlled Combustion Chamberage) designation.
Weatherby partnered with another machinist, and as they say, the rest is history. The .375 Weatherby appeared in the mid-1940s but was replaced in 1953 by the even more powerful .378 Weatherby Magnum. Weatherby reintroduced the .375 Magnum around 2002, and it has regained some acclaim.
My research all started when I had the chance to purchase a 1942-vintage Winchester Model 70 that was originally chambered for .375 Magnum but was rechambered in 1943 to .375-CCC. I’ve built six rifles for various wildcat cartridges, but the .375-CCC Model 70 is my first “ready-made” wildcat rifle.
The deal also included a set of RCBS reloading dies and 60 or so pieces of fired brass.
I already had a bunch of bullets and suitable propellants to choose from and plenty of Federal 215 Large Rifle Magnum primers for building the handloads. However, I quickly discovered that specific references to this odd wildcat round are sparse.
Phil Sharpe’s supplemented second edition of his Complete Guide to Handloading lists an extensive array of CCC cartridges from .218 Bee through .375 H&H Magnum. Norma’s website offers some interesting facts. And the revised edition of Jack O’Connor’s The Rifle Book from 1964 offered only one sentence in reference to the .300 Weatherby’s father being “a wildcat known as the .300 PMVF for reasons too complicated and obscure to go into in this limited space.”
But I had a plan. Because the .375-CCC cases appeared to be very similar to the .375 Weatherby Magnum, I had my gunsmith full-length resize a couple of the fired .375-CCC cases, and I carefully measured the critical dimensions before trying to chamber the cases in the rifle. The bolt closed with just a hint of resistance.
Next, I determined the .375-CCC case has approximately 12.5 percent more capacity than the .375 H&H Magnum, which suggested I could likely load the maximum .375 H&H recipes and stay within safe pressure levels. I did so with a couple of lighter-weight Speer and Sierra bullets. I then fired a whole box of Hornady 300-grain DGX .375 H&H factory ammo, and as expected, the average velocity was somewhat attenuated by the case expanding to fill the .375-CCC’s “improved” chamber.
A few weeks later I found—and purchased—a box of .375 Weatherby Magnum brass at a Carter’s Country gunshop. Sure enough, the new cases chambered easily with a snug fit in my Model 70’s custom chamber. The only evidence was a slightly burnished ring on the Weatherby cases’ uniquely shaped shoulders. My conclusion: For all practical purposes, the .375-CCC is the same as the .375 Weatherby Magnum.
Norma and Hornady handload manuals currently offer load data for the .375 Weatherby Magnum, and A-Square’s load manual also includes a few recipes for its 300-grain Dead Tough bullet. Plus, Hodgdon’s Reloading Data Center includes the round on the website. So I reloaded half of the Weatherby cases and some Winchester Super-X cases and compared the wildcat rifle’s results with shooting results for another of my vintage Winchester Model 70s, which is chambered for the .375 H&H Magnum.
Both Model 70s have factory-standard 25-inch heavy sporter barrels and actually weigh almost the same at about 9.5 pounds. Accuracy from the bench was almost identical for both rifles/cartridges, but velocities for the .375-CCC were higher by as much as 200 fps.
Other than following routine reloading procedures used to load any other big-bore belted cartridge, there is only one special caution to heed. You have to be sure to adjust your sizer die to headspace on the case shoulder (like you would with any bottleneck, beltless rifle case) to avoid repetitively stretching the body just above the case head when sizing and firing to avoid premature case separation.