I would guess the .270 Winchester but don't know for sure, even though I hunted and "discussed" rifles and cartridges a lot with Chub. He tended to like faster velocities in cartridges of .30 or under, and plenty of bullet weight in "medium bores."
Can specifically remember what he used on a few hunts we did together. Two were in Wyoming, first whitetails in the Black Hills where he brought a .300 WSM, and on a pronghorn hunt a few years later he used a .280 Remington Ackley Improved. Everybody did on that hunt, because it was an "invitational" deal when Nosler introduced the round as a factory cartridge--but he liked the .280 AI long before then, as well as one of its derivative wildcats, the 6.5/.280 AI---which he called the 6.5 Blow-Hole Express. On his last safari in 2011 (where I shared a tent with him) he took one rifle, a custom .375 Ruger.
Interestingly, he preferred the .223 Remington for prairie-dog shooting--which we did a lot of together. He had a custom .223 that he shot (often when very hot) until it wouldn't "group" minute-of-dog anymore. He roughly calculated that barrel had fired close to 20,000 rounds before he had another installed--and the rifling was just about gone for 7 inches in front of the chamber.
But I can ask Kevin, and see if he remembers.
