150 grain bullets will work fine. HOWEVER at 300 Mag Velloocity, they can do a lot of meat damage. If you don't mind the extra damage, go ahead and use them. The 180 grain is just a better choice for the 300 Win Mag. I know because I have tried both. If I were to use 150 grain bullets, I would load them down to about 2800 fps. JMO.