Ordnance Notes -- by Bob Stoner GMCM (SW) Ret.
XM21 7.62mm NATO Rifle (Sniper’s) with Sionics Suppressor
The XM21 or M21 7.62mm NATO Rifle (Sniper's) is an accurized M14 rifle. The M14 rifle is a product-improved version of the venerable M-1 Garand rifle of World War 2 and Korea. The major improvements of the M14 over the M1 were a 20-round magazine vs. an 8-shot clip; no more "last round" twang as the clip ejected; a charger or stripper clip guide which allows the magazine to be "topped-off" from 5-round clips while still in the rifle; a selector switch that allows semi-automatic or full-automatic fire; a redesigned gas system; a gas cutoff for launching rifle grenades; an efficient flash suppressor.
The M21 7.62mm Rifle (Sniper's) is derived from the M14 7.62mm Rifle (National Match). The M14NM has its selector shaft welded to permanently convert it to semi-automatic fire only. The action of the M14NM is bedded and its barrel is free-floated so that none of the operating parts contact the stock at any point. The trigger pull is adjusted to 4-1/2 pounds. The flash suppressor is reamed to prevent "flyers" (that is, bullets which are deflected from the normal path) caused by rain drops in the suppressor. The wooden stock is impregnated with epoxy resin to make it warp-free in high or low humidity conditions (a shrunken or swelled stock changes the rifle's zero). New 1/2-minute rear sights replace the 1-minute of angle rear sights and the front sight blade is reduced to 0.062 inch in width for long range shooting. The front band is permanently attached to the gas cylinder. The barrel is modified to prevent gas cylinder and operating rod sloppiness which would affect accuracy. The operating rod spring guide is changed from a stamping to a tapered rod so the spring will stack uniformly.
The M14NM becomes an M21 rifle with the addition of a scope mount and an adjustable ranging telescopic (ART) sight for daylight operations. The M21 uses the AN/PVS-2 or AN/PVS-4 passive night vision (starlight) scopes for nighttime operations.
The ART sight is a 3 to 9 power, Parkerized steel, nitrogen-filled telescopic unit that has a ballistic cam matched to the 7.62mm M118 Special Ball. The M118 Special Ball has a muzzle velocity of 2,550 feet/second and a 173-grain, full metal jacket boat tailed bullet. The M118 is effective out to 1,100 yards.
The Sionics suppressor was designed and manufactured by Military Armament Company of Alpharetta, GA. The Sionics suppressor replaces the standard M14 flash suppressor. Once the M14 flash suppressor is removed, the Sionics suppressor nut and split bushing are installed and suppressor is screwed onto the barrel. The purpose of the Sionics suppressor is to moderate the muzzle blast of the rifle (to make it hard to locate) and hide the muzzle flash at night. It is not a "silencer" in the classic sense, but it so reduces the muzzle blast that the noise made by the rifle extracting, ejecting, reloading, chambering, and locking is VERY apparent. The Sionics suppressor has a bleed valve to exhaust the gas from the suppressor after firing.
Snipers or other users of the M21 who were firing at night would fire one round into the ground and then apply tape over the muzzle of the suppressor. The combustion gases would be trapped and there would be no oxygen available to support a muzzle flash when the rifle was fired in anger that night. Snipers would use the gas cutoff to make the M21 a manually-operated rifle to eliminate the now noisy semi-auto action.
The maximum effective range of the M21 with the AN/PVS-2 or AN/PVS-4 starlight scopes is about 400 meters (440 yards). The maximum effective range of the M21 with the ART scope in daylight is 1,000 meters (1,100 yards). The sight mount can accommodate either the ART or starlight scopes without any loss of zero. Weight of the M21 with ART scope, Sionics suppressor, and a 20-round magazine is approximately 12.5 pounds. Changing from day to night optics adds another 2.5 pounds to the weight.
The M21 sniper rifle has been product improved into the M25 sniper rifle. The M25 adds a receiver lug to further minimize shifting in the stock. The scope mount is changed to a Brookfield Precision 5-point type; the inverted T-lug on the receiver (3 points), the charger guide (1 point), the forward receiver ring (1 point). The ART scope is replaced by a 10-power Leupold M3, M3A, or Mk 4 scope with Mil-Dot reticle. The stock is a modified M14A1 automatic rifle stock with an adjustable cheek piece. Naval Special Warfare units use both M21 and M25 sniper rifles today.
© 2005 Bob Stoner R3