The idea that a variable power scope is somehow less reliable is an old myth that surfaces from time to time. All of my hunting rifles are equipped with variable power scope, haven't experienced any problems with them what so ever. I cannot speak about the .325 WSM however I have used the .338 WM on elk almost exclusively, the old 275gr. Speer RN bullet was as reliable a bullet as I ever used on elk. Never lost a single animal, most never went more than a few steps.
