Skip to main content


Evaluating the FN SCAR 20S, the commercial variant of the U.S. military's Mk 20 SSR.


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.

A coalition Special Forces soldier fires a Mk 20 SSR from a hilltop during a firefight near Nawa Garay village in Afghanistan.

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.

The large and robust bolt carrier assembly is driven by the gas piston assembly. The charging handle is reversible.

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.

The two-position gas regulator can be accessed through a port in the extended monolithic receiver. Two settings are offered.

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.

The SCAR 20S stock is the same as on the MK 20 SSR and is easily adjustable for length of pull and comb height.

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 magazine is the same pattern as used on other SCAR 17 variants, although the SCAR 20S comes with one 10-round mag.

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. 

Notes: Accuracy is the average of five, five-shot groups at 100 yards. Velocity is the average of five shots across a LabRadar chronograph placed adjacent to the muzzle.


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,

Current Magazine Cover

Enjoy articles like this?

Subscribe to the magazine.

Get access to everything Guns & Ammo has to offer.
Subscribe to the Magazine

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Recommended Articles

See More Recommendations

Popular Videos

Cameras Don

Cameras Don't Lie: Subsonic 9mm vs. .300 Blackout

In this segment of "Cameras Don't Lie," a subsonic-ammo showdown, 9mm vs. .300 Blackout fired from AR rifles.

Trijicon RMRcc Reflex Sight – Perfect for Optics-Ready Concealed-Carry Pistols

Trijicon RMRcc Reflex Sight – Perfect for Optics-Ready Concealed-Carry Pistols

The people asked and Trijicon answered. Introducing the RMRcc miniature red-dot sight for compact, concealed-carry pistols. Trijicon's new RMRcc features the durability and reliable controls that have made the RMR so successful, but its reduced dimensions make the “Concealed Carry” model better suited for the popular small-frame pistols designed for discreet carry and personal defense.

All About .300 Blackout

All About .300 Blackout

The .300 Blackout is here to stay, and we take some time to look at new technology surrounding this cartridge. Next, we pit subsonic rivals against each other before stretching the legs of this CQB round out to 600 yards from a short 9-inch barrel.

Guns & Ammo TV: Wheelgun vs. Pistol

Guns & Ammo TV: Wheelgun vs. Pistol

In this segment of “Pros vs. Joes,” we put competitive shooter and author James Tarr against Guns & Ammo TV cameraman Nathan Wilt. With handguns, they see who can knock down plates the fastest on two Revolution Targets Heavy Duty Plate Racks. Here's the catch: Tarr has to use a Colt King Cobra in .357 Mag. while Wilt shoots a Smith & Wesson M&P9 M2.0 in 9mm.

See More Popular Videos

Trending Articles

The Winchester .350 Legend straight-wall cartridge is ideally suited for hunting hogs and deer; here's everything you need to know to make it work for you..350 Legend Cartridge: Everything You Need to Know Rifle

.350 Legend Cartridge: Everything You Need to Know

Tom Beckstrand - April 02, 2019

The Winchester .350 Legend straight-wall cartridge is ideally suited for hunting hogs and...

Small, lightweight and purpose-built for sub-compact carry guns, Surefire's XSC pistol light takes on EDC illumination segment.Surefire XSC Micro-Compact Pistol Light: First Look Tactical

Surefire XSC Micro-Compact Pistol Light: First Look

Jeremy Stafford - September 10, 2020

Small, lightweight and purpose-built for sub-compact carry guns, Surefire's XSC pistol light...

9 Commonly Misused Gun Terms How-To

9 Commonly Misused Gun Terms

Kyle Wintersteen

"Assault weapon." Sixteen-round "clip." A box of "bullets." When it comes to guns and gun...

Trijicon has dominated the Carry Optic landscape on hard-use handguns for years. With the new RMRcc, they plan on dominating the concealed carry market as well.Trijicon RMRcc Reflex Sight Review – Perfect for Concealed Carry Optics

Trijicon RMRcc Reflex Sight Review – Perfect for Concealed Carry

Jeremy Stafford - October 01, 2020

Trijicon has dominated the Carry Optic landscape on hard-use handguns for years. With the new...

See More Trending Articles

More Reviews

If you're in need of a pistol to bet your life on, look no further than the pistol that won over the U.S. Army, the SIG Sauer P320 - M17.Review: SIG Sauer P320 - M17 Reviews

Review: SIG Sauer P320 - M17

Richard Nance - August 14, 2020

If you're in need of a pistol to bet your life on, look no further than the pistol that won...

The upgradable Tikka T1x .22LR rifle is a great place to start on the growth chart to precision shooting success.Tikka T1x .22LR Rifle Review Reviews

Tikka T1x .22LR Rifle Review

Tom Beckstrand - October 05, 2020

The upgradable Tikka T1x .22LR rifle is a great place to start on the growth chart to...

The Hi-Point 995 TS carbine has low recoil, is chambered in a readily available cartridge, and is more accurate than many would expect when shot using loads it likes. It is a good choice for anyone in search of an inexpensive recreational firearm, or one for self-defense.Hi-Point Firearms 995 TS Camo WC Review Reviews

Hi-Point Firearms 995 TS Camo WC Review

Proofhouse - August 03, 2020

The Hi-Point 995 TS carbine has low recoil, is chambered in a readily available cartridge, and...

Ruger's latest PC Charger 9mm wants to be your next self-­defense pistol.Ruger PC Charger Review Reviews

Ruger PC Charger Review

Tom Beckstrand - September 25, 2020

Ruger's latest PC Charger 9mm wants to be your next self-­defense pistol.

See More Reviews

Magazine Cover

GET THE MAGAZINE Subscribe & Save

Digital Now Included!


Give a Gift   |   Subscriber Services


Buy Digital Single Issues

Don't miss an issue.
Buy single digital issue for your phone or tablet.

Buy Single Digital Issue on the Guns & Ammo App

Other Magazines

See All Other Magazines

Special Interest Magazines

See All Special Interest Magazines

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Phone Icon

Get Digital Access.

All Guns and Ammo subscribers now have digital access to their magazine content. This means you have the option to read your magazine on most popular phones and tablets.

To get started, click the link below to visit and learn how to access your digital magazine.

Get Digital Access

Not a Subscriber?
Subscribe Now