.375 in (9.5 mm)
.375 Winchester Wikipedia
The .375 Winchester is a modernized version of the .38-55 Winchester, a black powder cartridge from the 1880s. It was introduced in 1978 along with the Winchester Model 94 “Big Bore” lever action rifle.
Though very similar in appearance to the parent .38-55, the .375 has a shorter case length and operates at much higher pressures (50,000 CUP).