I bought a new 300 WSM Browning Xbolt for a elk hunt last year and only used it for a walking stick so far. But I used the Federal 180 Grain barnes bullets and never got to see how well they would work on a live target.
I have never had a 300 WSM but I can tell you what I've used for my 300 Weatherby, 300 Win. mag and my 338 win mag. I started reloading shortly after I got my Huskvarna 300 Win. Mag and I used 150 grain bullets, but I was using them strictly for deer. When I got ready to go elk hunting, I switched and loaded 180's. If I was going to use the same rifle for both elk and deer, I'd go with a 165 grain bullet.
For the 300 Weatherby mag. I used strictly 180 grain bullets and used them for both deer and elk. They are a great all-around bullet and I would still use those today if I used that rifle much. If I had a 300 WSM that I was going to use on multiple animals, I'd use the 180's. They work great on elk and sure do kill deer and antelope. If I was going to use the rifle strictly for elk, I'd go to a 220 grain bullet. They still have great trajectory and really do the job with knock down power.
For my 338, which I use almost exclusively now for both deer and elk, I load a 250 grain Nosler partition and it kills dead. I love how it performs in my Browning and what it does to animals. I have killed antelope, deer, bear, elk, moose, gemsbok, zebra, kudu and a few other animals with that same bullet and I have been very pleased. Some may say it's overkill on smaller animals, but I don't find that it destroys any more meat than my 270. I shoot it well and am not afraid of the recoil.
If I were you and I was going out after elk, I would load a 180 or above. I love the knock down power of a heavy bullet.
Ihunt.....I got a new 300 WSM last year and it actually took me a while to get a load put together that was consistent. In the end I was using Win. brass, RL17 powder, Federal Magnum rifle primers, and the Barnes TTSX Triple Shock (boat tail) in 180 gr. With this load I instantly killed my first elk from 250 yds., but shot placement was right on. I used the same load for mule deer and whitetail deer hunting as well. Great results. My brother has the same gun with a longer barrel, and his best load was Win. brass, RL17 powder, Win. magnum rifle primers, and Nosler Accubond 165 gr. This has been a great load for him.
Let me start by telling you the story of two Johns.
John number one went on a day hike with a couple of friends in the Cascade Mountains about an hour from Seattle. He somehow got separated from his buddies and became lost. John was dressed in casual cloths for a warm weather day hike and had nothing but a lunch with him. He spent three days in those mountains and luckily made it out to tell the story.
John number two, a friend of John number one, was much better prepared when...