The M4 carbine is a family of firearms tracing its lineage back to earlier carbine versions of the M16, all based on the original AR-15 designed by Eugene Stoner and made by ArmaLite. It is a shorter and lighter version of the M16A2 assault rifle, with 80% parts commonality. The M4 has selective fire options including semi-automatic and three-round burst (like the M16A2), while the M4A1 has a full auto option instead of three-round burst.