The SIG 551 – – The World’s Best Assault Rifle Now Available In Limited Supply, in the USA

Story and Photos by Leroy Thompson

The author fires the SIG 551 prone. With the 30-round magazine

The author fires the SIG 551 prone. With the 30-round magazine in place, a relatively high shooting position is necessary.

When I’m asked what I consider the best battle rifle in the world, my answer is fairly simple: the SIG 550. Although I sometimes qualify that by adding, “unless there’s a SIG 551 around.” Designated the “Stgw 90” in the Swiss Army, the SIG 550 has now been the Swiss military rifle for two decades, and it remains as good as ever. The SIG 551 is a variant that incorporates a few features I feel make it even more versatile.

I’ve been fortunate enough to have worked with a variety of military and police units and to have gotten to know many highly advanced collectors of assault rifles. As a result, I’ve fired most of the world’s assault rifles in either select fire or semi-auto versions with a few exceptions.

I have handled a Russian AK-100 but I have not fired one. Nor have I fired a Beretta ARX-160, Japanese Howa Type 89, Polish Beryl, Indonesian Pindad SS2, Malaysian LP 06, Croatian VHS, nor a Chinese QBZ-95 or QBZ-03. There are a few others that are just locally made versions of other rifles so I haven’t included them. Still, I think I’ve got a pretty good basis for comparison when it comes to assault rifles.

For anyone who might be wondering, I have shot the military version of the SCAR L and SCAR H quite a bit as well as the semi-auto civilian version, and I have shot the military versions of the Remington ACR and the Bushmaster semi-auto versions. Both are excellent rifles, and they incorporate some of the features that I believe make the 550/551 so good – but they aren’t a SIG 550 or 551.


What must be borne in mind with Swiss service rifles is that they are designed for a citizen army, most of which are reservists. As a result, the troops keep their rifles at home, along with an initial battle pack of ammo designed to get them to the front lines to fight. They shoot their rifles quite a bit, and the marksmanship is stressed.

SIG 551 Gun

The SIG 551 allows a second—or third—magazine to be coupled to the one in the mag well. The author recommends coupling just one extra mag on the left side as coupling an extra to the right side (as shown) will prohibit the stock from folding.

The classic story about the marksmanship of Swiss infantryman occurred during World War II when Switzerland faced a possible German invasion. A German officer was talking with a Swiss officer about Swiss neutrality and asked, “What would you do if a German Army three times size of the Swiss Army invaded?” The Swiss replied, “Each Swiss soldier would shoot three times!”

Because each Swiss soldier maintains possession of his rifle throughout his years of service and may have it converted to semi-auto for purchase after his service ends, he is more “invested” in it and expects to be issued a high-quality weapon. The SIG 550 more than meets this criteria. It is accurate, reliable and ergonomic.

Among the SIG 550’s features are a rotary diopter rear sight that allows accurate use from point blank to 300 meters or more, a folding stock that’s as comfortable in shooting position as a fixed stock, semi-transparent magazines that allow a quick check of remaining ammo. The magazines also clip together so a mag change may be made immediately to a spare.

Other outstanding features include an easily operated ambidextrous safety/fire control and a useful feature in Switzerland and elsewhere that sees cold winters: a trigger guard rotates to the right or left, allowing it to be fired while wearing mittens or heavy gloves.


The SIG 551 is the carbine version of the 550 with a 14.3-inch barrel as opposed to the 550’s 20.8-inch barrel. The 551 has been used by some special military and police units, especially in France where the Commando Hubert (French SEALs) and GIGN, among others, use it.

The semi-auto SIG 551 SP model has a Picatinny top rail and has imported into the USA a 16-inch barrel. Prior to the Clinton Assault Rifle ban, a few semi-auto 551 SPs were imported into the USA. I have heard figures as low as 25, but certainly, not too many more than that made their way over here. The last of these semi-auto 551s I saw sold brought $11,500.

the 551 Rifle

Here’s a good look at the business end of the 551. Note also the sling attachment point. This is not the standard barrel used on the Swiss 551s.


The SIG 551 SP has topped my wish list for many years. When SIG Sauer USA brought out the 556, especially the later version with the side-folding stock, I ordered one of the SWAT models and have been very happy with it, as it shares many features with the 551. Nevertheless, I hoped that SIG would be able to produce the 551 in the USA.

That hasn’t happened, but the next best thing has. At the point when the Clinton assault rifle ban went into effect, there was a shipment of SIG 551 SPs somewhere in the process of clearing customs, but due to the ban they could not be sold to civilians. I believe a few were sold to law enforcement agencies, but most sat in limbo in a bonded warehouse for years.

There were 250 of these SIG 551 SPs that BATFE witnessed having their receivers cut. Because of the ban on importing barrels, the barrels could not be used either.

Then SIG Sauer USA made uppers that were serial numbered to the 551 lowers. In addition to the receiver and barrel, other US-made parts included the monoblock, bolt head, bolt carrier, gas piston and trigger. The remainder of the parts were from the SIG 551 SPs. I would have preferred if the original Swiss barrel would have been used, but given the choice of no 551 or this hybrid one, I’ll take it. And, even though the compliance parts were made in the USA, they were made by SIG, so this remains a SIG-produced carbine.

Thompson fires the 551 on hanging plates at 100 and 200 yards

Thompson fires the 551 on hanging plates at 100 and 200 yards. Note that the gas valve is in Position 2.


I’ve always shot well with the SIG 550 using the diopter sights, but when I say “well,” that means two minutes of angle on a good day. Since the 551 has a top Picatinny rail, I decided to maximize the carbine with an optical sight. Since I use the Trijicon TA31 USMC Rifle Combat Optic (RCO) more than any other battle rifle sight, I decided it would be a good choice for the 551.

The RCO is a dual illuminated 4X sight with a red chevron aiming point. This chevron combines with Stadia lines to allow quick aiming to 800 meters without any adjustments. I have found the RCO very fast at close range where I bring the chevron up onto the target; or for precise shooting at longer range where I use the tip of the Chechen at 100 meters; or the interior of the tip at 200 meters, the top of the post at 300 meters and the stadia lines at longer distances. Bullet drop for a 62-grain M855 round is incorporated into the reticle.

Dual illumination allows the chevron to get brighter in sunlight and lighter in low light. In total darkness, the tritium insert illuminates the chevron and top of the post to allow easy aiming to 300 meters in pitch blackness. For target referencing, the Marines stipulated horizontal referencing lines on each side of the chevron and post. With practice, these may be used to lead a target.

As with other Trijicon ACOGs, the RCO is waterproof to 30 meters and fabricated with a tough military-grade aluminum housing. The Marines have used their RCOs in combat for years, and they are truly battle tested. With the flat top adaptor, the RCO went on the 551 quickly and was ready to zero.

SIG 551 Gun Magazine

The SIG 551 comes with an ambidextrous safety. Note the second magazine coupled to the one in the magazine well.


I took along some Guatemalan M193 surplus for general functioning tests, some ATI Turkish MKE 62-grain ammo, a couple of magazines of U.S. M855 green tip, and a box of Black Hills 77-grain long-range ammo. I zeroed the RCO at 100 yards with the 62-grain green tip as that is the load I will use with it most often.

Note that the RCO is designed for 100-yard zero as aiming at longer ranges is based on the optic being on at 100 yards. I have normally found the 77-grain Black Hills load especially accurate at longer ranges. In fact, using this optic on an M4 Carbine, I once shot a 500-meter group of less than 3 inches, but that was an exceptionally good day. Also, I can count on sub-Minute of Angle groups to 300 yards consistently with the 77-grain.

The 551 shot well with the Guatemalan surplus as I got groups just over an inch with it at 100 yards. At the same distance, the 77-grain Black Hills was producing groups just under or just over an inch and just over 2 inches at 200 yards. I also did quite a bit of shooting with the ATI 62-grain ammo because I have had some malfunctions with it in other guns and wanted to see how it worked in the 551 (see my comment below). At 200 yards, I fired 15 rounds prone quickly and put them into the chest area of the target.


At first, I was having feeding failures with each round—with all types of ammo. I assumed that the 551 might be dry, so I lubricated it, but that did not solve the problem. Eventually, I tried rotating the gas valve to Position 2, after which the 551 worked fine, including with the ATI ammo, which I have found in the past to be too light to function in some carbines.

Generally, Position 2 is designed to allow more gas volume when the weapon is fouled or iced, but in this case it was necessary for normal operation. It could be that the 551 will function on Position 1 once the parts wear in. It may also be that after I give the gas piston system a thorough cleaning, it will operate fine on Position 1.


All the other features I like on the SIG 550/551 series are on this carbine. The stock folds and unfolds readily and is very comfortable when locked open. The pistol grip is one of the most comfortable I’ve used and it incorporates storage for small parts or cleaning patches. I’ve always liked the SIG 550 safety, which is well located for operation with the shooting thumb. Ditto for the ambidextrous safety for shooting left-handed.

The 551 takes SIG 550 20- and 30-round magazines, which may be coupled to have two or three together. Generally, I do not couple them, but if I do, I only do two. It is generally more efficient to have the second magazine ride to the left of the mag well than to the right of it, as this allows the stock to be folded and allows a more efficient change with the support hand.


Initially, all of the SIG 551 carbines were available in black only, but I have heard rumors that over time, some green ones were made, although I have not seen one. The 250 limited-production 551 carbines assembled by SIG Sauer USA are to be the only ones of this type made and come with a limitation certificate. The sole distributor for the 551 was West Coast Armory.

Currently, SIG’s website shows that all of the guns have been sold. Some, however, are currently available on some of the internet auctions and other sites at around $4,000. Many will be satisfied with the SIG 556, which is an excellent rifle, but for those who have always wanted a SIG 551, this may be your last chance—unless U.S. import laws are changed substantially.

2 thoughts on “The SIG 551 – – The World’s Best Assault Rifle Now Available In Limited Supply, in the USA

  1. WHEN are we going to see the Swiss Arms 751 here ? I have an M1A and a 1/2 MOA Springfield Armory, Inc SAR4800 (Imbel FAL) and I’d probably trade them both for one 751…

  2. Hi,

    Can you tell me why there is a 16″ barrel?( my 551-2) Over here in Europe they use only the 14.3″ and the 17.9″.

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