USMC Door Gun - Afghanistan

Weaponsman brings a fascinating post on the door gun on the Marine Corps battle helicopters.

U.S. Marine Corps Lance Cpl. Matthew Ghibaudi performs a weapons check from inside a UH-1Y Huey helicopter before providing aerial assault support for ground convoys in Helmand province, Afghanistan, May 3, 2014. Ghibaudi, a crew chief, is assigned to Marine Light Attack Helicopter Squadron 369. U.S. Marine Corps photo by Sgt. Frances Johnson.

Some interesting info on their choppers as well.

The Marines are the only service still flying the 1950s-vintage H-1 Huey and 1960s-vintage H-46. But their Hueys have been rebuilt, zero-timed in fact; the airframes born as UH-1Ns were a twin engines (the Sea Services always wanted this for over-water reliability) version, unlike the Army’s old single-turboshaft H-1s (the Army equivalent being the UH-1D/H). Supposedly, 100 or so of the Y models are rebuilt Ns but the Marines have found it more economical to buy all-new airframes than to pay for Bell to disassemble, evaluate, repair and restore clapped-out N airframes, so a lot of these are all-new birds.

The UH-1Y and its sister, the AH-1Z, also have a fully articulating all-composite four-blade rotor system in place of the much simpler two-blade teetering rotor of the H-1, which inherited its rotor system, conceptually at least, from the 1940s-vintage Bell 47. The new rotor eliminates some of the low-G limitations and safety issues (look up “mast bumping”) of the original Huey rotor system. The old bird was safe within its flight envelope, mind; the new one just has a larger envelope. 

 I did not know what "mast bumping" was, so I looked it up.

There is also a hilarious military video on Youtube from the 80's that seeks to explain it, but I kept getting distracted by the antique verbal delivery of the people and the fact that no one had any computers on their desks.