The system was developed in-house under the direction of then Col. Jonathan Martir, PN (M) (GSC), N-6.
The first generation MSSR was deployed in 1996 as an M16A1 with a Tasco variable 3-9 x 40 mm rubber-coated scope on a DPMS Tri-mount atop the carry handle. This required a Delta HBAR cheek piece on the stock to align the operator's eye with the elevated scope position. The standard handguards were replaced with a free-floating aluminum forearm, and a Harris folding bipod was attached to the underside of the forearm. The standard M16A1 barrel was replaced with a free-floated 24" (68 cm) DPMS Heavy Stainless Steel Ultra Match barrel with a 1 in 8.5" right-hand twist, with an M16A1 front sight base. A J&P match trigger was installed.
The second generation MSSR was created by removing the forward portion of the carry handle and attaching the Tri-mount directly to the top of the upper receiver. The Tasco scope and scope rings were attached to the Tri-mount, which provided a lower scope-to-bore height. The Delta HBAR cheek piece was no longer required and was removed. The M16A1 front sight base was removed and replaced with a DPMS gas block. The barrel was changed to a DPMS Ultra Match barrel with a 1 in 8" RH twist, and the M16A1 stock and pistol grip were replaced with A2 versions.
The current third generation rifle retained the second generation features, but replaced the Tasco scope with a Bushnell variable 3-9 x 40mm scope with a Mil-dot reticle, mounted with three scope rings on the receiver-mounted Tri-mount. For the Philippine Marine Corps, barrel length remained the same at 24" with the 1 in 8" DPMS Ultra Match Barrel. A version with a 20" barrel was made available for the Philippine Navy Naval Special Warfare Group (NSWG).
More recently, the Government Arsenal under its present director, Major Gen. Jonathan C. Martir (Ret.), has been developing several further evolutions of the rifle as part of its carbine/rifle manufacturing project. The first of these is an updated model intended to replace the older 3rd generation rifles. Another new version is a designated marksman rifle/special purpose rifle (DMR/SPR) variant intended to "meet the requirement for a 5.56mm rifle to engage targets up to 800 meters with optics." This rifle would replace the older M14s currently in use as designated marksmen rifles in the Philippine Army. The new rifle will feature an 18" free-floating bull barrel with a 1 in 7" twist, a standard A2 flash suppressor, a flattop upper receiver with a Picatinny rail, provisions for a bipod and semi and select fire. The new variant, designated the "Government Arsenal SPR/DMR" is set to go into service in 2015, with the production of new rifles and the upgrading of older MSSRs to the new standard. In addition, 40 units of 16-inch designated marksman rifle variants are planned to be turned over to selected AFP Special Operations Forces (SOF) and the Scout Rangers for testing and evaluation. This carbine model features a railed upper receiver, a mid-length gas system, a Daniel Defense 16-inch cold-hammer forged barrel, a Daniel Defense free-floating railed handguard, a 4x32 Trijicon Advanced Combat Optic, a Magpul STR buttstock, a Hogue grip containing a cleaning kit and a cerakote finish.