M16A4

You have to get to a certain rank to unlock the M4, which is the fully auto version of the m16.

Hope this helps

There is no automatic M16 in Call of Duty 4. There is only the 3 round burst option. There is an M4 which was made as a lighter, and automatic M16.

There is an auto but you have to open up you're controller and cut the trigger spring

You probably saw a modded controller. They can be bought from things like ebay for $60 bucks or so.

This may sound stupid but I am not a nerd I watch to much tv. In the Vietnam war soldiers were using to much ammo because they were just spraying bullets on full auto. The military changed the m-16's to have a three round burst so that they did not just waste all their ammo. So bye bye fully-auto M-16

You need to understand that the M16A4 is a compromise weapon that was spec'd out by Aberdeen specifically to REMOVE full-auto from that weapon. Basically what they discovered in study of the M16 and the bullet-to-kill count during Vietnam was that when full-auto was available the person firing the weapon discharged more rounds in the air than on target.

The M16, M16A1 have a full auto selection, but the M16A2 at the request of the Marine Corps replaced the Full Auto with three-round-burst. The M16A3 was basically the same weapon as the A2 with all the improvements (stronger stock, thicker barrel) but with the Full Auto Setting rather than the burst setting.

The M16A4 is basically the M16A2 with improvements including the removable carrying handle, full length quad picatinny rail for mounting optics and other ancillary devices, and the servicing kit slot located in the butt with extra lube. The Colt M16A4 model RO945 uses the safe/semi/burst selective fire settings. In other words it is not supposed to be an auto fire weapon.