450. Check out the Black Widow projectiles website. They're based in Melbourne. If they doesn't list what you want, have a chat to John and he might be able to make them for you.

When used in handgun hunting, wide meplat hard cast projectiles are recommend to be kept below 1400 fps. The reason is that above that velocity the nose tends to deform on impact and then you lose the wide meplat effect. Can't see any reason why it would be any different in a rifle.
The whole point of a wide meplat hard cast is to get maximum penetration in a straight line, its not designed for expansion.