Thompson shoots 551A1 from behind cover. Thirty-round magazines limit how low he can get.

Regular readers of this column know I’m a big fan of the SIG 550 series of rifles. I’ve shot just about all of them, including the Swiss military Stgw 90, though I don’t think I’ve fired the SG 550 Sniper version nor the 553, the improved version of the 552, which I have fired.

Still, I’ve put a lot of rounds through the various configurations. I was in Switzerland when only a few units had received the SG 540 for testing and got a chance to shoot it. The 540 was the forerunner of the 550 series. Manurhin in France also produced versions of the 540, and I’ve shot those.

I always wanted to shoot a 542, which was chambered in 7.62mm NATO caliber, but my military contacts only had 5.56x45mm 540s available. The most noticeable difference between the 540 and 550 is probably the 540’s skeleton folding stock as opposed to the solid one on the 550.

So I’ve established I have some experience with the various versions of the SIG 550. My favorite is the 551 carbine. I especially like this in the original selectfire 14.3-inch barrel configuration, but that’s a military and LE gun only. But to be honest, I was always just about as happy with the 551 model that was imported into the U.S. in very limited numbers in semi-auto with a 16-inch barrel. Unfortunately, those pre-ban imports have been known to bring $10,000 or more when sold, which has precluded all but really serious assault-rifle collectors from owning a 551. SIG Sauer, however, has now fixed that.

SIG Sauer 551A1 with Leupold VX-R 1.5-4X20mm Patrol scope mounted. Note ambidextrous safety, paddle magazine release, and linked 20-round magazines.

The new 551A1 offers shooters a rifle that they can take to the range and shoot a lot or use as their combat rifle without worrying about mortgaging their house. Purists will grouse that the 551A1 isn’t really a Swiss 551, since the barrel is U.S. made, as are some other compliance parts and the upper receiver. That’s true, but the 551A1 is pretty close to the original.

And in at least one way it is better than most original 551s. Although some later Swiss 551s had a mount for optical sights, generally they did not come with a Picatinny rail. The 551A1 does.

SIG Sauer 551A1 with Leupold VX-R 1.5-4X20mm Patrol scope mounted. Note ambidextrous safety, paddle magazine release, and linked 20-round magazines.
FireDot SPR Reticle.

I have always considered the 550/551/552 folding stock the most comfortable folding stock available for shooting. In fact, when deployed, it is more comfortable than most fixed stocks. I like the slim 550-type forearm too, and find it feels very good when shooting. The 551A1 retains the polymer 550-style magazines. For some, this is a disadvantage as these magazines are more expensive than M16 magazines. My answer: buy a SIG 556, which takes M16 mags.

I’ve always liked SIG magazines, which are clear enough to allow a quick ammo check, link together readily, and are very reliable. I also prefer the paddle magazine release of the 551A1 to the M16-type button of the SIG 556. I have gotten used to hitting the paddle with the support hand when I use 550-type rifles.

Another note on 551A1 magazines: three or more magazines may be linked using the clever stud and channel system on each magazine, but I would not recommend linking more than two magazines. Three or more loaded magazines get heavy and, if carried with the middle one in the magazine well, the drill for switching magazines can get complicated. But two magazines give a quick immediate reload.

I generally carry a 550-type rifle or carbine with the left-hand magazine in the magazine well and the spare to the right of the receiver. I learned this to avoid catching on web gear. Others prefer to carry the spare to the left of the receiver.

Twenty- and 30-round magazines are available for the 551A1 and other 550-type rifles. I sometimes carry a pair of 20-round mags in the gun with non-linked 30 rounders in mag pouches. This allows me to go prone or otherwise get low more readily.

The 551A1 employs the long-stroke gas piston system used on the 550 and its descendants. The ability to run longer without fouling is usually cited as one of the major advantages of a gas piston rifle or carbine.

551A1’s gas valve, front sight, and flash suppressor. Valve is in standard position.

Based on my experience, this is the case with 550-type rifles. I have fired my 550 for hundreds, if not thousands, of rounds without cleaning it. At times, I even shot it until it started malfunctioning, then turned the gas valve to let more gas flow and kept shooting it for the rest of that session.

The 551A1 has the same type of gas valve. My Swiss military contacts always talked about the gas valve being especially useful to allow more gas in very cold and icy conditions—ah, soldiering in the Alps!

Speaking of soldiering in the Alps, because Swiss troops were known to sometimes use their stocks as climbing aids or to slam them into the ground to stop sliding, a lot of P90 receivers got torqued or damaged. As a result, later generation Swiss 550 series stocks were designed to break away if too much force was applied.

On pure aesthetics, the 551A1’s barrel offends me a little bit, as I am used to the “bubble” behind the flash suppresser on the 550 and 551. But I’ve already gotten over it. The 551A1’s barrel has a 1:7 twist, so it will handle M855 62-grain ammo or 77-grain Mk 262, Mod 0/1 quite well. It will also shoot M193 55-grain ball acceptably.

The 551A1 includes the front hooded post and rear diopter drum. However, since the 551A1 has a Picatinny rail, the rear sight is removable. I think the SIG diopter rear sight is one of the better iron sights supplied on a battle rifle. I have managed to shoot two MOA with it at 100 and 200 yards fairly consistently using my 550.

Controls of the 551A1 are well designed. The ambidextrous lever safety is very easy to work and sure. I also like the cocking handle, which protrudes enough to catch well with the palm of the hand or if necessary with the boot to clear a jammed case.

Good-sized sling mounting points are located for easy sling mounting. I like the Swiss military sling, which has clips that quickly attach or detach to these mounting points. One of my major criticisms of the 551A1 is that it does not come with one of these Swiss-type slings.

The 551A1’s dimensions help keep it handy and easy to carry. Overall length with stock folded is only 26 inches and with it extended 36.1 inches. It is possible to fire the 551A1 with the stock folded. Since the stock folds to the right, if a linked magazine is used, it will have to have the spare on the left. Weight without a magazine is seven pounds.

I have shot various 550-type rifles with a Trijicon ACOG mounted and may decide to use one on the 551A1, but as it happened I had just gotten in Leupold’s VX-R 1.5-4X20mm Patrol scope to test. At only 9.4 inches overall and 11.5 ounces, I felt it would not affect the handiness of the 551A1. Yet it offers a lot of scope, which includes Leupold’s usual durability features.

The FireDot SPR reticle incorporates a well-designed crosshair with both horizontal and vertical stadia lines to allow ranging and/or lead. The center red dot may be quickly illuminated by pressing a button on the scope, and brightness may be adjusted by continuing to press it.

The Patrol incorporates the motion detector Leupold is now including on some tactical scopes, which will turn the dot off the scope if not used for awhile or back on as soon as the rifle is moved. Based on sources I checked, it is available for under $600.

Once I had the Patrol mounted and zeroed, I did quite a bit of shooting with the 551A1. I used surplus 55-grain M193 initially to test functioning and get the scope close to on. Then I switched to M855 green tip for accuracy tests. With the M855 at 100 and 200 yards, I was around the one MOA benchmark.

Shooting from a rest, I had a couple of one-inch groups at 100 yards, but most were between one and two inches. Likewise at 200 yards, I managed one of 2.25 inches but most were over three inches. I did not shoot on paper at 300 yards, but shot at plates. I wish I could say I hit them every time, but prone I hit them about half the time.

The 551A1 is comfortable to shoot, and the stock and forearm are excellent, which aided accuracy. The 551A1 trigger is not as good as the triggers on any of the Swiss 550-series rifles I’ve fired. It is good, but not the aid to accuracy that the crisp trigger on my 550 is.

Every time I’ve taken the 551A1 shooting, reliability has been absolute, with no malfunctions of any type. I like it enough that I’ve already let my contact at SIG Sauer know I intend to purchase it. My 550 will get moved back in the safe, and the new 551A1 will be my shooter.

MSRP for the 551A1 is $1,599. While magazines will cost more than those for the 556, on the positive side SIG Sauer has them available. The 551A1 ships with two magazines. I recommend that anyone owning one have at least a couple of 20-round magazines and whatever number he considers sufficient of 30-round magazines.

For me, and I think many who will purchase one, the price is relative. This is about as close as most will get to owning a SIG 551. Yes, an AR-15 and magazines can probably be purchased for half as much, but many of us who like SIG rifles will decide it’s close enough to the original to give a lot of pleasure shooting it. And I expect to shoot it a lot.

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