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I am a successful hunter and have killed deer in other states with a .223 caliber rifle. Why can't I use my .223 to hunt deer in Washington State?

Big game, except cougar, must be hunted with a minimum of .24 caliber (6mm) centerfire rifle. Cougar may be hunted with a .22 caliber centerfire rifle. Rimfire rifles are not legal for big game.

In Washington, with the exception of cougar, a .24 caliber rifle is legal for all big game, including deer, goat, sheep, elk, and moose. Although it is okay to do so, few hunters actually use a .24 caliber rifle to hunt game larger than deer, due to the lack of knockdown power. The Washington Fish and Wildlife Commission did not want to establish a sliding scale of legal rifle calibers by species, so it opted for the .24 caliber rule.