for the infantry. Certain M27s are selected for accuracy; when provided with scopes and suppressors they are designated as the: M38 Designated Marksman Rifle. The rifles are distributed one per squad. Specifications The original test weapon was a modified M16A4 rifle with a free-floated 1:7 stainless steel match grade heavy barrel, a "Mil-Std-1913 modular rail system" (this most likely implies the use of the Knight's Armament Company Free-Floating Rail Adapter System) and an M16A1 trigger assembly (semi and full-auto functioning). A number of day optics were used initially, which included Hensoldt Blitz, Leupold CQ/T, ACOG, Leupold TS-30A1 and ultimately the Leupold TS-30A2. The test night optic was the AN/PVS-17B, apparently now being fielded with USMC combat units though the AN/PVS-22 is preferred. The later SAM-R was roughly a modified M16A4 pattern rifle: Upper & Lower Receivers: The lower and upper receivers are standard M16A4. The SAM-R has a standard M16A1 single-stage trigger installed, which allows limited use as an automatic rifle, ammunition permitting (See Mk 262 Mod 1), but there also have been examples using Knight's Armament (henceforth referred to as KAC) two-stage match triggers. The SAM-R is also equipped with a PRI M84 Gas Buster charging handle system and a Norgon ambidextrous magazine release. Barrel: The barrel is a long 1: twist match grade stainless steel barrel, manufactured by Compass Lake Engineering from Krieger blanks. Current SAM-Rs are equipped with 'chipped' flash suppressors to allow attachment of the KAC M4 quick-detach sound suppressor, while earlier examples were fielded with standard compensators. Sights & Optics: For iron sights, the SAM-R uses the KAC 600-Meter flip-up rear sight. The first SAM-Rs used a custom Quantico-built gas block with bayonet lug and Picatinny rail on top. A KAC flip-up sight was mounted on that rail. Some intermediate models used separate gas blocks and barrel attached bayonet lugs. Current rifles are built with a special KAC-made gas block that has both a flip-up sight and a bayonet lug. The issued day optic is the TS-30A2 (military designation for Leupold's Mark 4 M3 3-9 x 36 mm MR/T Illuminated riflescope) mounted with ARMS #22 high rings, the same configuration used with the Mk 12 Mod 0/1 SPR, though more recent photos indicate the four-power Marine Corps Rifle Combat Optic ACOG is also used at times. The folding front sight mentioned earlier was designed for use with the AN/PVS-22 Universal Night Sight. Handguard: The SAM-R