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Squad Designated Marksman Rifle
Soldiers from the3rd Infantry Division with SDM rifles.
Type	Designated marksman rifle
Place of origin	United States
Service history
In service	2004–2020
Wars	War in Afghanistan (2001–2021) Iraq War
Production history
Designer	United States Army Marksmanship Unit
Specifications
Mass	10 pounds (4.5 kg) with optic & fully loaded 30-round magazine
Length	39.5 inches (1,000 mm)
Barrel length	20 inches (510 mm)
Cartridge	5.56×45mm NATO
Action	Gas-operated (direct impingement)
Muzzle velocity	3,050 ft/s (930 m/s)
Effective firing range	600 metres (660 yd)
Feed system	20- or 30-round detachableSTANAG magazine

TheSquad Designated Marksman Rifle (SDM-R^[1]) is an Americandesignated marksman rifle used by theUnited States Army. It is essentially a heavily modifiedM16 rifle designed to provide U.S. Armydesignated marksmen greater accuracy and firepower at longer ranges, increasing aninfantrysquad's effective range to up to 600 meters.^[2]

The SDM-R is similar in development and role to theSEAL Recon Rifle andMk 12 Special Purpose Rifle (SPR), designed and produced for theUnited States Navy SEALs and theUnited States Special Operations Command respectively.

The SDM-R was replaced by theM110A1 SDMR, expected to enter service in the 2020s. In this role, the M110A1 retains the "Squad Designated Marksman Rifle" name.^[3]

The addition of an embeddedmarksman at theplatoon orsquad level has historically been a continuing process in theU.S. military. TheUnited States Marine Corps (USMC) experimented with this duringProject Metropolis, before creating the "Squad Advanced Marksman" (SAM) role along with theSquad Advanced Marksman Rifle (SAM-R) specifically for this purpose.^[4]

The3rd Infantry Division followed suit in implementing a training program to have one marksman per squad, the Squad Designated Marksman (SDM), and developing a rifle, the Squad Designated Marksman Rifle (SDM-R). The SDM is an integral part of the squad and serves as arifleman first anddesignated marksman second. The SDM is not meant to be a squadsniper who engages the enemy with precision fire at long ranges, but instead is trained to directly support the squad with well-aimed shots at ranges slightly beyond the normal engagement distances for riflemen.

Much like the U.S. Marine Corps SAM-R, the 3rd Infantry division SDM-R was anaccurized M16 rifle built in-house by theUnited States Army Marksmanship Unit with 240 rifles provided for deployment in Iraq.^[5] The rifle was informally known as "the AMU rifle".

The SAM-R has since been replaced in U.S. Army service, mostly due to the performance of match grade 5.56 NATO ammo in the DMR role.^[1] Its slated replacement was theHeckler & Koch HK417-basedM110A1 SDMR,^[6] expected to enter service in the early 2020s.^[7]

The National Guard Marksmanship Training Center of theArkansas Army National Guard conducts the fourteen-day-long Squad Designated Marksman Course atCamp Joseph T. Robinson. Soldiers fire over 1500-rounds from the M16A4 rifle under the close supervision of course cadre.^[8] Another is done in Fort Benning, Georgia.^[9]

Task Force Small Arms Readiness Group (TF SARG) conducts the week-long SDM course at the SARG academy atCamp Bullis,Texas.^[10] Many of the instructors arePresident's 100 recipients.

• The U.S. Army used either M16A2 or A4 lower receivers previously supplied by eitherColt orFabrique Nationale de Herstal.^[2] All rifles were equipped with a fixed A2stock and aKnight's Armament Company 2-stagematch grade trigger The upper receivers were flat top style, but unlike the SAM-R and SPR, they did not have extended feed ramps.
• Barrel: The 1:7twist, 20-inch (510 mm)barrel from the M16A2 and A4 were replaced with astainless steel Douglas Barrels 1:8 twist, 20-inch barrel, with 12 flutes cut into the barrel to reduce weight. The front sight block was installed with 4 set screws instead of two taper pins. The SDM-R retained the A2-styleflash hider.
• Sights and optics: The issuedoptic was a 4×32Advanced Combat Optical Gunsight (ACOG) (models TA31F, TA31RCO, TA01, TA01B, or TA01NSN).^[11][12] A Matech Industries 600-meter backupiron sight was also used.
• Handguard: Daniel Defense DDM4 Rail 12.0 handguard, with an octagonal aluminum collar locking it to the upper receiver.^[2] The handguard provides a free-floatingPicatinny rail forend.
• Bipod: A Harris S-Lbipod attached to an ARMS #32 throw-lever rail mount was mounted to the underside of the handguard.^[2] Since the handguard was free-floating, it did not come into contact with the barrel, and any pressure from the bipod on the handguard did not deflect the barrel.

The82nd Airborne Division examined an alternate version, based on theM4 carbine. The barrel was to have been an 18-inch (460 mm) longfluted Douglas barrel with 1:8 twist. A mid-length gas system was to be used, along with the Daniel Defense M4Rail 9.0 handguard. This effort never went beyond the staffing process.

Wikimedia Commons has media related toSquad Designated Marksman Rifle.

• Squad Advanced Marksman Rifle
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• 5.56×45mm NATO semi-automatic rifles
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• Military equipment introduced in the 2000s

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