Building a Vietnam-Era M21 Sniper Rifle

How the writer recreated the Army's first semi-automatic sniper rifle from a Springfield M1A.

By Robert A. Sadowski | Published Nov 8, 2017 8:52 PM

Guns 101

The M14 and It’s Shortcomings

The M14 was pretty lousy battle rifle, but on paper, it seemed the logical progression from the M1 Garand. Tweaking the M1’s operating system, chambering the rifle in 7.62x51mm NATO, and attaching a detachable 20-round magazine were great improvements over the M1.

Where the M14 fell flat was the select fire feature that offered semi-automatic fire or full automatic fire. In full-auto mode, the M14 was nearly uncontrollable.

The M14 rifle replaced the M1 Garand and proved to be more effective as a sniper rifle than a combat weapon. *photo courtesy Springfield Armory National Historic Site*

My pals who were given a free ticket to Southeast Asia by President Johnson liked the M14 compared to the then-new M16 rifle. The .30 caliber 7.62 round (.308 Win) offered plenty of power compared to the also fairly new 5.56x45mm NATO round used in the M16.

But there were other considerations—in the jungles of Vietnam the M14 was long, heavy, and hard to quickly maneuverer, and the wooden stocks didn’t fair too well in the wet, humid jungle climate.

What many soldiers and Marines—they were called grunts back then—appreciated about the M14 was its utter reliability, accuracy, and knock-down power. My pals told me they typically kept the M14 set on semi-auto fire.

The war in Vietnam proved the M14 was too long and heavy for the close jungle guerrilla style fighting. The wood stock swelled in the humid environment knocking the weapon out of zero. A fiberglass stock was a temporary fix (and one that ultimately came too late to be useful) but the real solution was the M16, which was by design lighter, had less recoil, and was better suited to the close to mid-range combat encountered in Vietnam. Plus, its synthetic furniture was mostly impervious to moisture and humidity.

Briefly a Battle Rifle

As a service rifle, the M14 had a short tenure. It was introduced in 1959 and was phased out by the M16 from 1966 to 1967. War had changed from the open conflicts of WWII where a rifle like the M1 Garand excelled, to close, urban and guerrilla fighting where the advantage went to a lighter, more compact rifles firing smaller, faster rounds like the M16 and AK-47.

Soldiers in Vietnam armed with the M14 rifle. *photo from steamcommunity.com*

However, that wasn’t the end for the M14.

The thing is, the M14 is really an excellent rifle. In semi-auto it’s accurate, allows for fast followup shots, optics are easily mounted, and it is extremely reliable like the M1 Garand before it.

A New Mission

While the M16 had many advantages as a general issue rifle, there was a real need for quality sniper rifles during Vietnam. Commercial civilian Winchester and Remington bolt-action rifles topped with scopes were the norm, the Army also turned its attention to modifying the M14, reviving the platform as the X21M sniper rifle. The Marine Corps chose to focus on bolt guns for their sniper rifles.

In 1969, Rock Island Arsenal took about 1,500 National Match M14s (target grade rifles) and mounted what was then a high tech optic, the Redfield 3-9x ART (Adjustable Ranging Telescope). The ammo chosen was 7.62x54mm NATO XM-118 match ammo. A new sniper rifle was born.

All told, the M14, renamed the XM21 with a specially selected walnut stock, proved to be a better sniper rifle than battle rifle when it was first fielded in the second half of 1969.

Making a Sniper Rifle

The XM21 used a National Match Barrel for accuracy, original wood stock, and a high magnification scope. *photo courtesy Springfield Armory National Historic Site*

The Rock Island Arsenal tuned the M14s ensuring the national match barrels were uniform and with minimal head spaced, the wood stock was dried and impregnated with epoxy as well as glass bedded. The internals were polished like the piston, gas cylinder and the action was smoothed up. Triggers were set at 4.5 pounds. According to Army tests these rifles grouped under 10 inches at 900 meters.

The gun’s aforementioned optic, an ART Redfield Accu-Range 3-9x40mm commercial scope, was designed by James Leatherwood in 1964 and was unique in that the ART mounting system automatically adjusted as the magnifier zoom ring was rotated, meaning a cam system in the scope physically raised or lowered it as the zoom was rotated.

The Scope

Two U.S. soldiers in Vietnam, the left with an M16A1 and the other with a scoped M14 rifle. *photo from pinterest*

The original ART used a 2nd focal plain reticle featuring strata marks that covered 30 inches at 300 yards which allowed for range estimation. For the shooter it was easy. Zoom in on the target—30 inches is roughly from the top of the head to the belt line—and the the cam would raise or lower the scope to compensate for the range. The ART automatically computes the bullet trajectory as target is ranged so the shooter only has to aim at the target dead-on with no hold over. All the shooter needs to compensate for is wind.

The original scope mount was developed by the Army Marksman Unit as the X21 and consisted of a one-piece weaver style base that attaches to the side of an M14’s receiver via a large thumbscrew. It also mates with a side groove in the receiver for more stability. The offset mount is necessary because the M14 ejects empty casings from the top of the receiver and wasn’t originally designed for optics.

A reissued M21 rifle, in use in Iraq, 2006. *photo from modernfirearms.net*

The M21 and M25 Today

Eventually, the wood stock was replaced with a synthetic one and the XM21 sniper rifle was officially designated the M21 in 1975. Since then, it has been in continuous use in the U.S. military, though it was officially replaced by the M24 Sniper Weapon System in 1988, which is based on the bolt action Remington 700 rifle, though a number of M21 rifles were reissued in Iraq.

As the M21, the M14 lives on in various configurations as a supplement to the M24 and as the M25.

The M25 Sniper Weapon System was a joint venture sniper rifle built for the U.S. Army Special Forces and the U.S. Navy SEALs in the early 1990s. It was originally developed by the 10th Special Forces Group to fulfill a requirement for a sniper rifle based on a match grade M14 that satisfied the requirements of both the Army Special Forces and the Navy SEALs.

Here a spotter and shooter team use an M25 the modern equivalent to the M21. Note the lightweight Harris bipod attached to the rifle. *photo courtesy Springfield Armory National Historic Site*

SOCOM called the rifle the “Light Sniper Rifle,” and it is also known as the “Sniper Security System.”

The commercial version has been named “White Feather” in honor of Carlos Hathcock, the U.S. Marine Corps sniper who became famous during the Vietnam War. The enemy gave Hathcock the nickname, White Feather, and placed a bounty on his head. Hathcock wore a white feather in his boonie hat, daring the enemy to spot him.

The M25 is very similar to the M21, except for certain details. The rifle features a National Match M14 barrel in a McMillan glass bedded fiberglass stock. It uses a special gas piston, a National Match spring guide, and a Brookfield Precision Tool Advanced Scope Mounting System.

The M25 is topped with a variety of optics, since SOCOM operators have an amount of latitude when choosing their gear. The M25 is not a replacement rifle for the M24 Sniper Weapon System, but was was designed to fill a specific need for spec ops troops and has been in service since the Gulf War.

Building a Vietnam-Era M21

The mount allows empties to eject with ease. *author photo*

I wanted to get a feel for that original XM21 sniper rifle, and much like the U.S. Army did back in the 1960s, I cobbled together an ersatz Vietnam Era sniper rifle using a Springfield M1A rifle as a base, a Hi-Lux M1000 ART reproduction scope, and an ARMS side-scope mount. This is probably as close to a Vietnam-era setup as I could get using modern equipment and not hunting down vintage components.

The Loaded M1A rifle from Springfield Armory was chosen as the base for the M21 build. *mfg photo*

For the rifle, I chose the Springfield Armory Loaded M1A model with a wood stock because it’s already pretty similar to the M14, other than not having a full-auto mode, of course.

The Springfield uses a rotating bolt operated by a gas piston. When a round is fired, gas from the round is siphoned from the barrel and used to move the piston. The Loaded model features a medium-weight premium air gauged National Match barrel and a two-stage trigger tuned from 4.5 to 5 pounds. This is close the original except for the glass bedding, epoxy-impregnated stock and a few other tweaks.

A Modernized Scope

Hi-Lux optics makes an updated replica of the famed Leatherwood ART scope. The magnification zoom ring is actually fitted to cam to achieve ranging without hold over. Courtesy Hi-Lux Optics.

mfg photo

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Hi-Lux Optics (hi-luxoptics.com) manufactures a replica of the ART scope, called the Leatherwood M-1000 2.5-10x44mm. This optic uses a more modern Mil-Dot reticle that can range 18-inch targets. All the shooter needs to do is frame an 18-inch or 1 meter target using the strata marks on the reticle using the zoom dial and the scope automatically ranges the target and compensates for bullet trajectory out to distances from 250 to 1,000 meters. No holdover. No guesswork.

Hi-Lux also adds their multiple zero technology, which allows the scope to have up to five different zeros so you can swap the scope onto another rifle, or zero multiple loads. Think of the Leatherwood M-1000 as an updated ART.

The Scope Mount

The Sadlak, Leatherwood and M1A combined are a modern interpretation of a Vietnam Era XM21 sniper rifle. *author photo*

Sadlak Industries (sadlak.com) in my opinion manufactures the best scoop mount for the M14 and M1A. Sadlak builds an improved version of the Brookfield Tool and Machine mount, which was made in the 1990s. They offer the mount in steel, aluminum, and titanium versions—I stuck with the steel model.

Critical to attaching the Sadlak mount is how the male tab fits into the female groove of the rifle receiver. *author photo*

The M14 was never designed to have a scope mounted to it, so the process of mounting a scope is a bit different than say mounting a scope to a flattop AR. Depending on the manufacturer of the rifle, the left side groove may or may not be cut to military spec. If it’s not, it can cause the mount to not mate properly to the receiver.

Sadlak sends an inspection kit with every mount so you can be sure it works.

The handguard of the M1A is fiberglass, while the stock is wood. *author photo*

Additional Tweaks

Keep in mind, when mounting a scope to an M14, the stripper clip guide must be removed.

The stripper clip pin is removed with a punch and hammer with the gun disassembled and the stripper clip guide is slid out of the dovetail.

When I mounted the rifle, I wanted a bit more cheek weld. Since the M14 wasn’t meant to work with a scope, the tube may end up pretty high depending on your stature and build. I added a BlackHawk! Urban Warfare IVS check pad to compensate, which raises the comb for a better weld.

With the stripped clip pin punched out from the inside of the receiver, the stripper clip can be removed to attache the Sadlak scope mount. *author photo*

Range Test

I laser bore-sighted the rifle and tested it at 25 yards just to see where it was hitting.

I then moved to 100 yards and used a bench rest. This is no lightweight rifle. At over 11 pounds with scope and mount, it could definitely be called “heavy” and it settles rather well on long shots.

I always seem to have odd amounts of .308 Winchester cartridges—hunting and target loads—so I fired a few of these orphan rounds to warm up the barrel and break in the rifle’s action. I like the recoil in the M1A, since the rifle is heavy and the cycling of the action seem to absorb a lot of it.

The M1A is equipped with a slotted flash hider similar to what original M14 muzzle devices. *author photo*

Those initial groups with random ammo were good. Then I loaded up Black Hills 168-grain BTHP, which had a muzzle velocity out of the M1A of 2663 fps. My average 5-shot group measured 1.26 inches. Nice.

Changing over to Hornady Match loaded with 178-grain BTHP bullets I noticed the groups opened up .25 inches on average. Muzzle velocity was 2590 fps.

This M1A seemed to prefer 168-grain bullets, so the next magazine was loaded with Norma USA 168-grain Sierra HPBT and the groups again closed up with my best group at 100 yards measuring 1.1 inches.

The Norma clocked at 2670 fps at the muzzle. Not the typical sub-MOA groups you would expect out of a bolt gun, but definitely accurate. Since I initially had access to only a 100 yard range, I zeroed the first tic mark above the horizontal strata, which means the center cross hairs would be approximately zeroed for 250 meters.

The M1A has a two stage trigger that is factory set at 4.5 pounds. *author photo*

My next trip was to test the new ART scope at distance. It was humid. One of those days when you feel like you are wading through the air.

I used a barren stretch of land and used a range finder to place a human-sized target at the known distance. All I had to do was frame the target in the tic marks, which confirmed the distance, allow for wind, and press the trigger.

I found I could easily hit the human size target. Even in the sweltering heat with sweat stinging my eyes. The rifle did my bidding. The more I shot it, the more I came to appreciate what those snipers did back in Vietnam.