My Grandfather was Edward Baden Powell (who also went by E. Baden Powell and Baden Powell). He and Ralph Waldo Miller co-invented and patented the Powell Miller Venturi Freebore (PMVF) design (patent 2,455,080 Nov. 30, 1948).
They accomplished this by rechambering an existing rifle to accommodate an oversized case machined to their design. They set up a company rechambering rifles and selling dies.
Interestingly, 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, Powell and Miller sold their company to Hollywood Gun Shop. That company offered the same service but gave the concept a different label—the CCC (Controlled Combustion Chamberage) designation. Weatherby subsequently partnered with another machinist, and they produced the .375 Weatherby.
I know that Lyle Corcoran, who owned Hollywood Gun Shop, was an acquaintance of my Grandfather and his company made CCC dies but I am not sure if he rechambered the rifles or if that was done by another company. VARD is stamped on the rechambered firearms and I do not yet know if VARD, Inc of Pasadena, who produced drafting machines, calipers and other measuring equipment made them under contract of if there was another company named VARD that did the machining.
The CCC cartridge was available in many different calibers from the .218 Bee though the .375 H7H magnum including .219 Zipper, .223, .243, 250-3000, .270., 30-07, .300, 6mm, 7mm and others. I have seen CCC dies marked Hollywood Gun Shop and others marked RCBS (these may be the original PMVF dies).
My brother and I own Winchester model 70 rifles chambered in CCC. One is .300 CCC and the other is .375 CCC. We have dies for both made by Hollywood Gun Shop.
Neither of us has fired these rifles but my Father did when he was working for my Grandfather as part of E. Baden Powell and Sons. They did a significant amount of ballistics testing in the 1940’s and my Grandfather wrote a technical bulletin containing graphs and charts, based on the ballistics testing, entitled "Killing Power" which was published by the NRA in 1944.
E. Baden Powell had several other firearm inventions and patents mainly for shotguns (he competed in .410 and 12 ga trap and skeet and was well regarded). He is probably best known for the invention of the Power-Pac which was marketed and sold by his friend and bsiness partner Frank Pachmayr of Pachmayr Gun Works.
The information here on the PMVF and CCC was corroborated, and some details filled in by, the following articles:
“.375 CCC Reloading Data” by Lane Pearce, March 18, 2019 - Shooting Times
“Don't Be Afraid of an Obscure Cartridge: The obscure .375-CCC wildcat round is eerily similar to and has a historical connection with the .375 Weatherby Magnum” by Lane Pierce Feb 9, 2019 – Shooter’s Gallery: THE RELOADER