Updated 27 March 2010

Twin 0.50" (12.7 mm) BMG
Picture taken aboard USS McCain DDG-56 in June 2002
Note that this weapon is produced in both Left and Right versions
US Navy Photograph No. 020604-N-5362A-007

Overhead view of twin 0.50" (12.7 mm) BMG
Note the 25 mm Mark 38 on the right
    Picture taken in the Gulf of Aden aboard USS Normandy CG-60 in May 2005
US Navy Photograph 050514-N-5526M-012

Preflight inspection of 0.50" (12.7 mm) BMG GAU-16 light-weight aircraft version on a SH-60 Seahawk helicopter
Picture taken aboard USS Kitty Hawk CV-63 in May 2002
US Navy Photograph No. 020507-N-9043G-001

Water-cooled 0.50" (12.7 mm) BMG about 1940

US Army water-cooled 0.50" (12.7 mm) BMG
Photograph courtesy of Scott Burris of the 381st Bombardment Group (Heavy)

Army Quad Mark 31 mounting on USS Lexington CV-16 in 1945
The helmet of the operator can just be seen in the center of the mounting.  Note the gun smoke from the upper left barrel.
National Archives (NARA) at Seattle, Photograph Record Group 181, 13th Naval District:  Records of the Naval District & Shore Establishments Ship Files ca 1940-1950 Box 21, CV16

Another Army Quad Mark 31 mounting on USS Lexington CV-16 in 1945
Note the small fuel tank on the rear of the mount, used to power the training and elevation motors
National Archives (NARA) at Seattle, Photograph Record Group 181, 13th Naval District:  Records of the Naval District & Shore Establishments Ship Files ca 1940-1950 Box 21, CV16

Gunner's Mate 3rd Class Jeff Healey, 23, from Albuquerque, NM, tests the barrel spacing of a BMG M2 with the "go/no-go" key in April 2003
This picture brings back memories of my doing exactly the same procedure about thirty years ago.  Hey, Jeff, two or three clicks, right?  Also, note how Jeff is getting ready to grip the cocking handle.  You grab the handle palm-up, not palm-down, with your thumb on the end of the handle.  That way, should the gun accidentally fire, you won't break your thumb.
US Navy Photograph No. 030412-N-1050K-014

 0.50" (12.7 mm) BMG on standard tripod mount August 2004
Note the barrel carrying handle, which aids in barrel changeouts - those barrels get hot!
     US Navy Photograph No. 040818-N-1755G-004

Twin air-cooled 0.50" (12.7 mm) guns
This weapon is now at the Polish Army Museum,Warsaw
Photograph copyrighted by Michal Kopacz

Inspecting 0.50" (12.7 mm) ammunition
Red tips indicate tracer rounds
US Navy Photograph No. 070225-N-6326B-031

An interesting picture showing the blank adaptor
The adaptor reduces the muzzle size, slowing the escaping gasses and thus causing a recoil "kick" large enough to cycle the weapon
US Navy Photograph No. 070821-F-8678B-034