.300 WSM vs .30-378 Weatherby
A to-scale size comparison of the .300 WSM and the .30-378 Weatherby, drawn from SAAMI and C.I.P. cartridge dimensions and aligned at the case head.
.300 WSM (left) beside .30-378 Weatherby (right), shown at the same scale.
The .300 WSM has an overall length of about 2.86″ with a 0.309″ bullet. The .30-378 Weatherby runs about 3.75″ on a 0.308″ bullet. That makes the .30-378 Weatherby about 1.3x the overall length of the .300 WSM. See the full reference for each: .300 WSM and .30-378 Weatherby.