FN SCAR 20S

Photos by Mark Fingar

The Special Operations Forces Combat Assault Rifle (SCAR) program began in 2002 with the goal of replacing the M4A1, the standard-issue AR carbine; the Mk 12 series of precision rifles in 5.56 NATO; the Mk 18, a 10.3-­inch barreled close quarters battle carbine; and the SR-­25 series of 7.62 NATO sniper support rifles (SSR). After several years of testing and evaluation, the Special Operations Command (SOCOM) fielded the FN Mk 17, sold commercially as the semiautomatic SCAR 17S.

The FN Mk 17 is a service rifle chambered in 7.62 NATO that has been in service for years on all fronts on the War on Terror. However, this most-­fielded version of the SCAR program is the one variant that had no similar peer on the replacement list. No lightweight 7.62mm rifle was in service before the Mk 17, which is part of the reason it has been so popular.

The second most-­fielded SCAR variant is the Mk 20 SSR. The SSR is supposed to replace the SR-­25 series, which includes the Mk 11 and M110 within SOCOM. SOCOM leaves fielding of the Mk 20 SSR up to individual units and, to date, the Mk 20 SSR is extensively fielded within the Naval Special Warfare (NSW) community and the U.S. Air Force Special Tactics Squadrons (STS).

While the Mk 17, Mk 20 SSR and the new commercially available SCAR 20S are all chambered in 7.62x51mm, there are some extensive differences between the Mk 17 and the longer-­barreled Mk 20 SSR/SCAR 20S. Inside the receiver, the Mk 20/SCAR 20S has a longer barrel extension and receiver tenon. The change is easily seen when comparing the four-­screw tenon on the Mk 17 with the six-­screw tenon on the Mk 20/SCAR 20S. The longer tenon and barrel extension were necessary to lend the Mk 20/SCAR 20S some additional rigidity between the receiver and barrel. The longer barrel and intended use with a suppressor put additional stress on the extension and tenon, so some extra beef was in order.

Despite the differences in barrel attachment, the Mk 17 and the Mk 20/SCAR 20S share some common barrel DNA. Both barrels are hammer-­forged and chrome-­lined, so barrel life is excellent. Barring serious abuse, a life north of 10,000 rounds should not be unexpected. The barrel used on the Mk 20 and SCAR 20S is longer than the one on the Mk 17 and features a heavier contour. This helps mitigate the effects of heat during extended firing strings and decreases the likelihood of a point of impact shift when using a suppressor.

Like the Mk 17, the barrel of the Mk 20 and SCAR 20S has a 1:12 twist rate, an interesting choice for rifles intended for long-­range use. Guns & Ammo editors saw no issues during our accuracy testing at 100 yards. However, groups at long range while using heavy 175-­grain bullets struggled due to the increase in transonic instability. This only became visible at 800 yards and beyond.

The commercially offered SCAR 20S featured here, like the Mk 20 SSR, has a two-­stage Geissele Super SCAR trigger. When the first Mk 20 SSRs were fielded, each rifle shipped with both of FN’s single-­stage and two-­stage triggers. This left the operator the choice of which trigger to use. Shortly after they first entered service, all triggers were replaced with Geissele two-­stage triggers by FN. Geissele triggers remain in service to this day and come standard with the new SCAR 20S.

The Mk 20 SSR has proven to offer tactical advantages beyond the SR-­25s they have begun replacing. The Mk 20 (and SCAR 20S) has a continuous top rail that replaces the two-­piece arrangement of receiver, and forend found on almost all SR-­25 and AR-­10 variants. The monolithic upper ensures that any clip-­on night vision devices are perfectly aligned with the riflescope. The more perfect the alignment, the less point of impact shift the rifle will experience with installation of a night vision device or thermal.

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The Mk 20 and SCAR 20S also feature an adjustable gas block. There are two settings for suppressed and unsuppressed shooting. While smaller 5.56 NATO rifles function just fine without an adjustable gas block — with and without a suppressor — the larger 7.62mm rifles benefit greatly from this feature. The extra gas produced from the 7.62mm’s larger case capacity, and resulting increase in bolt velocity, needs the additional regulation that an adjustable gas block provides.

The 6-inch-longer forend on the Mk 20 and SCAR 20S has optional sections of Picatinny rail that attach and host anything that will mount to Picatinny rail. These sections won’t see widespread use in the civilian sector, but military units need them to mount rangefinders, infrared lasers and illuminators.

A huge Mk 20 SSR improvement over the SR-­25-­pattern rifle is that it replaces a highly adjustable buttstock. The length of pull adjustment is a feature that the SR-­25, Mk 20 and SCAR 20S share. It is needed so the soldier shooting the rifle can account for body armor — worn frequently, but not always — and layers of clothing. (Remember, rifles see use in both hot and cold environments). However, the adjustable comb height is unique to FN’s SCAR rifles.

Adjustable comb height is essential for any rifle that will be used for observation. The SCAR 20S and its military sibling fall into the category of a Sniper’s Support Rifle, hence the military’s acronym SSR. These rifles are not intended to be a sniper rifle or a battle rifle. Rather the Mk 20 SSR serves as a designated marksman (DM) rifle. DM rifles are used in overwatch roles all the time, so supporting the shooter’s head during extended periods of observation is a must. The Mk 20 SSR makes this possible and the SR-­25 rifle it replaces does not.

Far from semantics, the difference between a sniper rifle and a DM rifle is the level of training the man wielding it has and the range to which the rifle will see use. DM rifles are used at shorter ranges and the men shooting them get an average of three weeks of specialized marksmanship training. Snipers get at least eight weeks and, as far as rifle skills are concerned, must hit smaller targets at longer distances.

The military’s Mk 20 could be a sniper support rifle or DM rifle because of its 7.62mm chambering, 1:12 twist rate and 20-­inch barrel. However, this combination limits its effective range to about 800 yards. Still, the SCAR family of rifles is modular and has easy- to-switch chamberings, so the Mk 20 SSR could be molded into a true sniper application by simply rebarreling it in a longer-­effective-­range cartridge, such as 6.5 Creedmoor. This modification would extend the range of the rifle by 200 to 300 yards. To date, FN America has made no indication that they intend to do so.

The FN SCAR 20S represents a civilian version of SOCOM’s modern sniper doctrine. The sniper’s main rifle is going to be chambered in .300 Winchester Magnum (WM), .300 Norma Magnum (NM), .338 NM, or .300 Precision Rifle Cartridge (PRC). The Mk 20 SSR already in the field is chambered in 7.62 NATO, but SOCOM is currently transitioning to 6.5 Creedmoor. The Mk 20 SSR and SCAR 20S are virtually the same rifle, about 1-­MOA accurate (tested by FN before it ships), extremely durable, and based on a platform that has been serving on the battlefield for several years. It is a proven design.

It will be interesting to see if the SCAR 20S makes the transition to 6.5 Creedmoor with the rest of SOCOM, or if it remains a 7.62 NATO option only. Regardless, for those looking for a known performer in the designated marksman realm or interested in owning a historic rifle that SOCOM uses, the FN SCAR 20S is now available for the rest of us. 

FN SCAR 20S

Type: Short-stroke gas piston
Cartridge: 7.62 NATO
Capacity: 10+1 rds.
Barrel: 20 in., 1:12-in. twist
Overall Length: 40.6 in. (collapsed), 42.5 (extended)
Weight: 11 lbs., 4 oz.
Stock: FN SSR, adj.
Grips: Hogue
Length of Pull: 13 in. (collapsed), 15 in. (extended)
Finish: Flat Dark Earth; anodized
Trigger: Geissele Super SCAR; 4 lbs.
Sights: None
MSRP: $4,500
Manufacturer: FN America, 703-288-3500,
fnamerica.com