Confusion of terms.
"Which rifle is bigger?" A rifle has a barrel and an action and a stock. It is chambered for a specific "cartridge".

.270 and .264 are just numbers.

.270 Winchester and .264 Winchester Magnum are two "cartridges".

.270 Win. is a bigger diameter (bullet) than a .264 win. mag.(bullet)

In most factory loadings(for the same bullet weight) the .264 win. mag. is a little faster than the .270 win. But out where the lead hits the meat I doubt if the hunter or the game can tell the diffrence between them.

I have hunted for many years with a .264 win. mag. and shot a lot of various big game with it.

Robin