Hello, I am a American Rifle named the M16 or if you want to pronounce it longer, it is the M16A1. I am a AR-15 style rifle. My caliber is the same as the M4, my sister, 5.56mm. I use the 5.56x45 NATO and my barrel length is 20 inches. I have a burst function in me. And my service started in 1964 to today. And my brother is the AR-15, and my sister is the M4. The AR is shoots once per trigger pull. And the M4 is automatic.