Mike: I killed a moose last year with one shot through the lungs with my .338 Magnum. The moose was 100 yards out, and after the first shot I didn't even load the chamber again, because by then the moose was dropping on its chest. It took maybe two second for it to drop. I shot it with a 230-grain FS. I have also done the same thing by hitting the moose to break the shoulder (at 200 yards). The results have been the same. The bullet also clipped the top of the heart when I shot that one on the shoulder.
What I have found out so far is that if the moose is not aware of my presence when I fire my rifle, it usually drops pretty fast. However, if I spook the moose before I fire my rifle it may walk a few yards. I have been extremely lucky, because only one moose (the largest one I have killed) I spooked before I shot it, and even so it only walked about 25 yards. I could be wrong about all this, of course, but so far that is what has happened to me.
The .338 sure packs a good punch, and the more I use it on game the happier I am with it.