The Modular Sniper Rifle, or MSR, is a bolt-action sniper rifle developed and produced by Remington Arms for the United States Army. It was introduced in 2009 and was designed to meet specific United States Army and USSOCOM Precision Sniper Rifle requirements. The MSR initially won the PSR competition and was called the Remington Mk 21 Precision Sniper Rifle in U.S. military service. However, it was then decided that the Mk 21 did not conform to SOCOM requirements at the time in 2018, and the program was re-competed with the Barrett MRAD selected in 2019 as the Mk 22 Advanced Sniper Rifle solution. The Remington MSR is a manually operated bolt-action weapon with a rotary locking bolt. To facilitate calibre change, the bolt is equipped with removable bolt heads, with bolt faces matched for appropriate calibres. Bolt heads have three radial locking lugs. The MSR rifle is built upon an aluminium alloy "chassis", which hosts a compact receiver, adjustable trigger unit, pistol grip, and fully adjustable side-folding buttstock. The quick-change barrels are free-floated inside the tubular handguard which is provided with a number of user-installable Picatinny type accessory rails. The top of the receiver also is fitted with a monolithic Picatinny rail used to install sighting equipment (telescope sights or night vision sights). Additional equipment includes a detachable folding bipod and a quick-detachable suppressor which installs over the specially designed muzzle brake.
The model that won the PSR competition is a modified version of the original MSR. It can be chambered in 7.62×51mm NATO, .300 Winchester Magnum, and .338 Lapua Magnum. It is reported to have 0.7 MOA average accuracy at 1,000 m (1,094 yds) with both Barnes and ATK 300 gr (19.4 g) .338 Lapua Magnum ammunition. Changes to the PSR version include:
Reinforced AAC muzzle brake for Titan QD, suppressor, Chromoly steel .338 barrel with 1:9.5 twist, 5R rifling, and Melonite (ferritic nitrocarburized) finish, one-piece handguard with 20 MOA top rail, barrel nut accessible without removing the handguard, X-treme trigger. Lightweight, removable buttstock with throw lever adjustments instead of ratcheting adjustments
On 14 August 2014, the Army announced it was seeking sources to produce .338 Lapua armour-piercing (AP) ammunition for use in the Mk 21 PSR to effectively engage targets out to 1,500 m (1,640 yds). The main objective is for the rifle to defeat level IV body armour at 400 meters, whether suppressed or unsuppressed, in temperature ranges of −65 to 160 °F (−54 to 71 °C). Other minimum requirements include a projectile velocity of 1,340 ft/s (410 m/s) or more at 1,250 m (1,367 yds), 1,000 ft-lb (1,356 J) of kinetic energy at 1,500 m (1,640 yds), and the ability to defeat both 3⁄8 in (9.5 mm) of rolled homogeneous armour (RHA) and 1⁄2 in (12.7 mm) of cast iron at 800 m (875 yds).

▪️ 🛠🇺🇸 Manufacturer Remington Arms
Unit cost $15,000
▪️✅ Produced 2009–present
▪️⬇️ Mass 13 lb (5.9 kg) (base rifle)
17 lb (7.7 kg) (complete)
▪️📏 Length 36 in (91 cm) (stock folded)
46 in (120 cm) (stock extended)
▪️➡️ Barrel length 20 in (51 cm)
22 in (56 cm)
24 in (61 cm)
27 in (69 cm)
▪️⏫ Cartridge
.338 Lapua Magnum
.338 Norma Magnum
.300 Winchester Magnum
7.62×51mm NATO
▪️🔁 Action Bolt-action
▪️⏭ Muzzle velocity
1,002 m/s (3,290 ft/s) (.338LM)
938 m/s (3,080 ft/s) (.300WM)
890 m/s (2,900 ft/s) (.338NM)
841 m/s (2,760 ft/s) (7.62 NATO)
▪️🔝 Effective firing range 1,500 m (1,640 yd) (varies on cartridge)
▪️⏬ Feed system Detachable box magazine:
5 or 10 rounds (.338 Norma/Lapua, 7.62 NATO)
7 rounds (.300 Win Mag)
▪️⏺ Sights Schmidt & Bender 5–25×56 PMII
Leupold & Stevens Mark 4

Ref: Wikipedia; cgfm.