The .400 Whelen cartridge was developed by Colonel Townsend Whelen while he was commanding officer of Frankford Arsenal in the early 1920s when he necked up the .30-06 to .40cal. In sportingclassicsdaily it was noted ”Whelen’s .400 suffered from a dearth of .411-inch bullets. It is also out of step with the current trend to slender rocket-shaped bullets for shots spanning zip codes. Still, it’s an efficient round and, with 300-grain bullets at 2,250 fps, adequate for any beast. While reformed 30-06 cases have enough shoulder to headspace, the original shoulder diameter was .458-inch, not .441, per the 30-06.”
