Now my two cents, (Which are actually worth about 0.0075 cents U.S.), my best friend will not use anything but a .303. He has owned a .300, and still has a .243 for varmints. But he loves that old clunker. We swaped on a synthetic RamLine stock, mounted a nice 3-9X scope, and it will clover leaf three shots at a hundred yards! His rifle weighs in less than my sweety, a .338. But, one of my all time favorite cartridges is the .270, it holds a sweet spot in my heart. The last one I've owned was a FN that was a pig to carry, but the old friend I bought it off of used it on everything from Coyotes to Grizzly and everything in between. It will, as the .303, kill anything that walks crawls or swims. For deer, either one would work great if you keep it within range of your rifle. Bear in mind, most guns will shoot fairly accuratly out to stupid range, but your bullets are specilized tools. By this I mean the .303 is a lower velocity, limited range rifle in classifacation. .311 & .312 dia. bullets are designed to expand at certain velocities. While you may hit your target at 400 yards your bullets may or may not expand properly, thus not assuring a clean kill. People do it, but I wouldn't advise it. As for my choice in guns, I feel that a fellow should shoot as big a gun as he (or she) can comfortably handle. I hunt in the rockies, and bears are the wild card there. Thats why I use a .338. I just feel more comfortable carrying a little extra insurance. I hope this helps a little.