Defense Media Network

Marines Seek Machine Gun Rail Space Enhancement

Marines looking for more "rail estate"

While U.S. real estate appears to remain an uncertain proposition, the tactical “rail estate” market has never been hotter, as the explosion of Mil Std 1913 weapon accessory mounting rail – a.k.a. “Picatinny rail” – mounting surfaces on weapons still seems to fall short of user demand, triggering rail space enhancement efforts.

The latest examples can be found in two recent requests for information (RFI) released by Marine Corps Systems Command (MARCORSYSCOM) in Quantico, Va. The two RFIs, sponsored by MARCORSYSCOM’s Product Manager for Optical Systems, call for input on an “In-Line Night Vision Device Rail Space Enhancement” for the M249 5.56mm light machine gun and M240B 7.62mm medium machine gun.

In both cases, the RFIs express interest in potential production of an in-line solution that would provide additional “rail space” on the weapons to allow in-line night vision devices to be attached in front of the current day optics used on those weapons.

In the case of the M249, for example, the Marine Corps currently employs the SU-258/PVQ squad day optic (SDO), a fixed 3.5X optical aiming sight (In 2009 the Marine Corps selected the TA11SDO-CP; Trijicon ACOG [Advanced Combat Optical Gunsight] 3.5 x 35 scope) that assists in engaging targets out to 1,000 meters. The SDO is also issued with a miniature reflex sight (RM05) for targeting close or rapidly moving targets.

M240B with MDO

Lance Cpl. Kyle Prather, a team leader with 2nd Battalion, 5th Marine Regiment, sights into his M240B machine gun during a firefight, May 30, 2012. The Marines engaged enemies with machine guns, sniper rifles, mortars and tanks.
The Marine Corps is seeking information on devices that would increase rail space on the M249 and M240B enough to allow the use of clip-on inline night vision devices that would mount in front of the existing day optics. U.S. Marine Corps photo by Cpl. Timothy Lenzo

The Marine Corps uses the SU-260/P fixed 6X optical aiming sight as the machine gun day optic (MDO) for use with the M240B (TA648MDO; Trijicon ACOG 6 x 48). Provided as a targeting tool to facilitate engagement of targets out to 1,250 meters, the optic is also issued with a miniature reflex sight (RM05) for targeting close or rapidly moving targets.

Both RFIs identify a number of performance attributes for the notional in-line rail space enhancement designs, with both threshold and objective attribute levels identified.

Not surprisingly, the attribute list specifies that any design solutions will be compatible with the weapon and will not interfere with weapon function, barrel exchange, or loading and unloading of the host weapon.

Another set of attributes addresses mounting designs.

In the case of the M249, for example, it notes, “If the design solution mounts to the M249’s feed mechanism assembly cover, it shall utilize hand operated throw levers with at least one integrated secondary lock that does not come apart into smaller pieces when attached or detached from the accessory rail…If the design solution utilizes hand operated throw levers, the operator shall be provided the capability to adjust the amount of tension on the locking throw levers to optimize initial fit to the accessory rail.”

The M240B attributes differ only in the caveat of whether the design mounts “on the optical sight cover assembly.”

Other attributes limit how much any new design can affect mounting locations for the current SDO and MCO day optics as well as the minimum number of “recoil grooves” to be provided with any new design solution (“no less than 24” for the M249 and “no less than 23” for the M240B).


Scott Gourley is a former U.S. Army officer and the author of more than 1,500...