I live in Missouri. According to the methods allowed this is what is on the website:

Centerfire pistol, revolver or rifle using expanding-type bullets. Legal ammunition includes lead bullets, copper bullets and bullets made of other material designed to expand.

It doesn't mention any particular caliber so I take it to mean .223 would be fair game. Although, I'll still research. If anyone knows for certain for Missouri, then please feel free to enlighten me. Thanks for the replies.