The .375 Whelen cartridge (A.K.A. 375-06) was developed in 1951 by L.R. "Bob" Wallack and named in honor of Colonel Townsend Whelen. It is a .30-06 Springfield case necked up to .375. While the .375 Whelen retains the .30-06's shoulder angle of 7' 30", an improved version was introduced with a 40' angle, providing more case capacity as well as better headspacing. The .375 Whelen Improved is favored by most.