heavier barrel, the Mk 48 Mod 0 is still 17% lighter and 8.4% shorter than the M240. The disadvantages of Mk 48 Mod 0 are that the life of the receiver is only about half of the M240B, and the effective range with accuracy are slightly lower than the M240B. The Mk 48 Mod 0 is currently in service with certain USSOCOM units, such as the U.S. Navy SEALs and Army's 75th Ranger Regiment. Variants Mk 48 Mod 0 This is a 7.62×51mm NATO version of the Mk 46, used by USSOCOM when a heavier cartridge is required. It is officially classified as an LWMG (light weight machine gun) and was developed as a replacement for the Mk 43 Mod 0/1. The M60-based machine guns are a great deal more portable than the heavier M240-based designs used elsewhere in the U.S. military in the infantry medium machine gun role. The M60-based designs have a long history of insufficient reliability, however. Trials conducted through the mid-1990s led the U.S. Army to replace its M60 with M240B GPMGs. The M240B weighs in at ~27.5 lb and is about 49 inches long with the standard barrel. Due to this extra weight and size NAVSPECWAR was reluctant to give up the increased portability of the M60 (~22.5 lb, 37.7 inches OAL with the shortest "Assault Barrel") designs, despite the M240's increased reliability. A request was put in for a new machine gun in 2001, and FN responded with a scaled-up version of the M249 weighing in at ~18.5 lb with an OAL of ~39.5". This new design achieved much better reliability than the M60-based weapons while bettering its light weight and maintaining the same manual of arms as the already in-use M249. USSOCOM was slated to begin receiving deliveries of the new gun in August 2003. Mk 48 Mod 1 The Mk 48 Mod 1 is an update of the Mk 48 Mod 0, which is also made in FN-America. Like the Mod 0, it is essentially an M249 scaled up to fire the 7.62×51mm NATO round. The Mod 1 utilizes a 19.75-inch barrel, weighs in at 18.37 lb unloaded, and has a rate of fire of 500–625 rpm or 730 +/-50 rpm. Major changes include the use of an adjustable buttstock, modified rail interface system, removal of the original hinged heat guard in favor of M249-style ones attached to the barrel, and modified