There was a test done where the same barrel was chambered first to 300 H&H, then to 300 WSM. In summary, they're pretty much the same cartridge in different shapes.
Hopefully Mule Deer will elaborate. Typing on this phone is distracting me from tonight's episode of Inspector Morse.
Gunsmith Charlie Sisk performed that experiment, at my request for an article in HANDLOADER. It's probably also mentioned somewhere in one of my books, but can't remember which one. He first chambered a barrel for the H&H, then tried several handloads with different powders and bullets, recording velocity, strain-gauge pressure and accuracy. This was all done on the indoor range he had in Texas ( he's since moved back to his native Kentucky), so temperature was consistent and wind non-existent.
He then rechambered the same barrel for the .300 WSM, using the same throat placement, but obviously having to cut off the rear of the barrel some. He fired the same bullets and powder charges, under the same conditions, and the results were just about exactly the same--including which loads shot most accurately.
