Welcome to the WSM madness. I have had one in the past. For your yardages I think you would do well with a mono metal bullet like the Barnes, Hornaday GMX, or the Nosler E-tip. I usually don't suggest these bullets, but since you are only going to 600 max, there is no need for a heavy bullet. If you run the mono metal bullet in a 165-180 grain, you will be good for those distances no problem. You can run a 165 over 3100fps maybe more. If you want to stick with a traditional lead bullet, then go with a bonded bullet of some type.
Now as for caliber... let me muddy the waters. So I know you are stuck on the 300WSM train, but why don't get off at the next stop and take a peak at a couple different 7mm's. I think you would be well suited for the 284 Winchester, and 7mmSAUM. The Saum will use about 10 grains less powder and shoot almost the same speed as the WSM. It is a very efficient little round and will do very well. Now for the .284 Winchester, it is a rebated rim that will work on a standard bolt face. It will send the 140-160 with near magnum speeds and give you better barrel life than the magnums. My uncle has killed many whitetails with this round for a couple decades in his old Winchester lever. He has since retired the rifle, but it worked very well. Both of these rounds are not all that popular and a little different from the norm. So there is my $.02 worth. Crunch these numbers and I think you'll be impressed.
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