The best bullet ever made for the .338 WM was the Speer 275gr. Semispitzer. In most .338's, it shoots like a match bullet, yet will penetrate lengthwise through a big B.C. or Alaskan moose.
: Unfortunately, Speer chose to discontinue this wonderful bullet. If you can find some in a gun shop, buy them and give them a try. At 2,600fps to 2,650fps, they're an incredible game bullet. IMR 4350 is a good powder for them, or a ball powder of similar burn rate.
: I have quite a number of friends with .338's who are hording their remaining supply of these bullets for their Moose and Elk shooting. They've run the gamut from Partitions to other available bullets, but are sold on the big Speer for all serious work. One such friend visited yesterday, asking me if I knew where he cold get some more, as he tried the remaining 5 he had on target from a rifle I'd just re-stocked for him last Spring. His 250gr. Noslers and 225gr. Hornady's were going into 1-1/4" and he thought there was something wrong with the bedding. Those 5 remaining 275's went into 3/8", just as they always had.