SIG M5 Spear Deep Dive: Is This a Good US Army Rifle?
Forgotten Weapons
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The NGSW (Next Generation Squad Weapon) program began in 2017 to find a replacement for the M4, M249, and 5.56mm cartridge. It came to a conclusion in April 2022 with the formal acceptance of the SIG M5 rifle, M250 machine gun, Vortex M157 optic, and the 6.8x51mm cartridge. SIG released a handful of civilian semiauto M5 / Spear rifles and thanks to Illumin Arms I have one to examine.
The rifle (Spear is its commercial designation; M5 is the military one) is an evolution of the SIG MCX, which is in turn an evolution of the AR-15 and AR-18 systems. The MCX move the recoil spring assembly into the top of the upper receiver, allowing the use of a folding stock. It also has very easily swapped barrels and a suite of fully ambidextrous controls. Scaled up to AR-10 size and chambered for 6.8x51mm, the MCX became the Spear.
That new cartridge (commercial designated .277 SIG Fury) is designed to produce high muzzle velocities out of short barrel (the M5 has a 13 inch barrel).It does this by boosting the operating pressure up to an eye-watering 80,000psi, which required the development of hybrid case using a stainless steel case head. This allows the case to handle those pressures safely. The currently available commercial ammunition is loaded to lower pressure, however. Much of the military and civilian use of this rifle will be done with downloaded training ammunition, which uses a conventional all-brass case.
Both the M5 and M250 were ordered by the Army with suppressors on every weapon, a significant advancement in Army policy. The can is another SIG development, entirely made using additive manufacturing and designed specifically to prevent gas blowback into shooters' faces (which is succeeds at wonderfully).
Overall, I believe the M5 / Spear is an excellent rifle - soft shooting, reliable, and very accurate. However, that does not mean it is the right rifle for the Army. Will its ability to defeat modern body armor prove worth the tradeoff in extra soldier combat load weight and reduced ammunition capacity? Only time will tell...
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