"In the Marine Corps, every man is a rifleman, but it seems the days of the full-length rifle with the USMC may be coming to a close. The M4 Carbine, pending approval by the commandant, will likely become the general issue weapon of the Corps, replacing the M16A4 for the infantry, Marine Corps Times reports:"
The M-4 is shorter and lighter. It is slightly less accurate at distance because the barrel is shorter.
Click to see a video comparing the two weapons.
I carried a weapon similar to the M-4 in Vietnam. The Marine Corps did not have this weapon. The rifle had been kicked off a shot up helicopter that had recovered an Army unit. My boss had gotten the weapon and he gave it to me when he left Vietnam. I carried it while in Vietnam and got a lot of attention from Marines who had not seen a weapon like this.
Our unit was the last Marine ground unit to leave Vietnam in June 1971. They told us to turn in all of our weapons 36 hours before we were scheduled to leave. "Screw that", I thought, and kept the rifle just in case the bad guys decided to attack. I gave the weapon to an Army truck driver as I left to get on the freedom bird back to the world, thus returning the weapon to the Army. Wish I still had it. Wish I had a photo of the rifle - never occurred to me to take a picture.
I think this was the rifle - it looks like it - U.S. ASSAULT RIFLE SMG GAU - 5A/A 5.56MM S XM177 (Colt model 649) without the forward assist. Complete with 20-round detachable box magazine.