Back in 1945-1946 Charles O'Neil, Elmer Keith and Don Hopkins developed a cartridge they named the 333 OKH which was based on the 30-06 case necked up to 333 caliber. It was a very good big game cartridge, but today it suffers from the lack of good, readily available .333" diameter bullets. When the .338 Winchester Magnum was introduced in 1958, it was followed immediately by a variety of commercial .338" diameter bullets. Shortly there after, several individuals at different places conceived the idea of either altering their 333 OKH's or necking up 30-06 to accept .338" diameter bullets. Since .338" diameter bullets are available in weights varying from 200 grains up to 300 grains, this makes the 338-06 a versatile and effective big game cartridge. The performance of the 338-06 is very similar to that of the 35 Whelen except that the .338" diameter bullets offer a somewhat better sectional density,- .313 for the Sierra 250 grain .338" Spitzer Boattail, as opposed to .279 for the Speer .358" spitzer bullet of the same weight. n summary, the 338-06 is an excellent big game cartridge, but not as flexible or versatile as the 35 Whelen in the matter of available bullet types. 

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.