I like the way the 215 and 200.20x jackets open at almost any velocity, but I honestly don't care what it is provided it meets the following criteria;
It has to shoot consistently reasonable.
It needs to perform in my expected velocity window.
It needs to be available.
I have several 300's and they all have a slight different preference for ammo. The 215 and 200.20x, 225eldm, 200ab and 180ab are all first choices in one of them.
If I have a finicky 300....I feed it a partition. The partition is not sexy on paper for bc, but inside 600 it's a great first choice.....and it NEVER fails.