There is no "S" in my 300WM. Full length shell for me. In regards to the 338WM comparison I was thinking factory 338WM versus a max powder reload with a 200 gr bullet. Those numbers are an even match and the sectional density of 200 gr 30 cal bullet is stout. I almost bought a 338WM but really think the 300WM fits my needs perfectly. The Savage I got is a .5 MOA gun from the factory so I couldn't be happier.