Question: what is the difference between an m16 and an ar-15?
Answer: The M4 and M16 are fully automatic, and they must be to qulify as such, but the AR-15 is the semi automatic version of the M16, in today's gun world that is all the distinction, it could have any barrel length but as long as it is semiautomatic and is still an AR/M16 type rifle it is considered to be an AR 15.