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The SIG SG 550 (SturmGewehr) is a Swiss assault rifle designed by Jürgen Baumann[1] and Ennio Mattarelli around 1978 and produced by Schweizerische Industrie-Gesellschaft since 1986; production of the rifle is currently handled by SIG Sauer AG (formerly SAN Swiss Arms AG) with the privatization of SIG's firearms division in 2000. Based on the previous SG 540, the SG 550 is the current service rifle of Switzerland.

History[]

During the 1970s, the Swiss Armed Forces's service rifle was the SIG SG 510, adopted as the Stgw 57. However, by the 1970s, the rifle was deemed as becoming quite dated, and a program was launched to find a replacement. An emphasis on modularity and weight reduction was placed, with the weapon family supposed to include a number of variations on the original design, such as a full-length assault rifle and a carbine used to mount rear-echelon troops.[2]

Over the entire program, the solicitation was ultimately narrowed down to two designs: the SG 541 from SIG and the SG C42 from Waffenfabrik Bern, the latter of which used an experimental 6.5mm cartridge. The 6.5mm and the SG C42 were ultimately rejected in 1981 in favor of the 5.6×45mm cartridge. A decision was made to adopt the SG 541 in 1983, and the rifle entered service in 1986 with the Swiss Army. The designation of "SG 541" was changed to the current designation of SG 550 in October 1983, while the carbine version of the rifle was thusly named the SG 551. Full production of the rifle began in 1986, with the rifle officially being adopted in 1990 as the Stgw 90.

After SIG's firearms division was privatized in 2000, production of the SG 550 series of rifles was handed over to SAN Swiss Arms AG (now SIG Sauer AG). 600,000 rifles were delivered as of 2012.[3] Fully-automatic versions of the SG 550 series of rifles are available on request from SIG Sauer AG.[4]

Design Details[]

The SG 550 is a long stroke gas-operated assault rifle which fires from a closed bolt. The rifle's action is essentially a downscaled version of what was featured in the SG 540 battle rifle; these use burning gases forced through a port in the barrel to power the weapon's moving parts. Once the gases enter the cylinder, these pass through an L-shaped channel in the piston head which directs the gases towards the gas valve; these force the piston and bolt carrier to their rearward position. As the action moves rearwards, the supply of gas is cut off as the gas port and L-shaped channel move out of alignment; any unneeded gas is bled out through an exhaust port in the gas cylinder. The weapon has a gas valve with two settings; one for normal operation and another for situations where heavy fouling or icing has occurred.[5]

The weapon is hammer-fired and features a four position fire selector; safe, single fire, three-round burst and fully automatic. A rotating safety guard is present on the weapon which can be flipped down to prevent the accidental activation of the fully-automatic fire mode when the user intends to fire in bursts only. The trigger guard is able to pivot to allows its users unhindered operation when using winter gloves.[5]

The SG 550 feeds from lightweight box magazines made of a translucent polymer. The magazines normally used have a capacity of 20 rounds, although 5- or 30-round magazines are also available. The weapon features a side-folding skeletonized buttstock which locks into a stud on the handguard; some versions feature a folding bipod made of an aluminum alloy which folds into grooves in the lower handguard. The SG 550 features a bolt hold-open device which locks the bolt open when the gun is empty; the shooter can simply lift the bolt catch lever on the left of the rifle or tug on the charging handle.[5]

Most parts of the weapon are made of steel while the handguard, stock and pistol grip are made of a high-strength polymer; the gas system's components are made of stainless steel. The barrels are cold hammer forged steel which is gas nitrided, hardened and tempered; they are fitted with birdcage flash hiders. The upper receiver has the capability to mount optics or other attachments.[5] All rifles are test-fired for accuracy and function before leaving the factory.

The rifles are equipped with iron sights adjustable for both windage and elevation, consisting of a rear diopter drum with a hooded front post on the gas block. A Kern 4×24 optic is installed for designated marksman use; this type of sight was already used on the SG 510.[6] The rifles come standard with a spare magazine, cleaning kit, sling and a loading aid for rapid firing.

The rifles can be fitted with Stgw 90 bayonets produced by Victorinox and by Wenger in the past before the former acquired Wenger. With the right adapters, the SG 550 can be fitted with the Eickhorn KCB-77 or American M9 bayonet.[7] Full-length rifles can be fitted with the SIG GL 5040 or 5140 underbarrel grenade launchers, while carbine-length rifles can be fitted with the compact GL 5340 grenade launcher.

Variants[]

Military[]

SG 550

Original length variant. Adopted in 1990 as the Stgw 90 (Sturmgewehr) in Switzerland and the F ass 90 (Fusil d'assault) in France.

SG 550 SR

Also known as the SG 550-1.[8] Accurized version of the SG 550 designed specifically for Swiss security forces. Introduced in 1988. Features a lighter two-stage trigger, a heavier hammer-forged barrel, a new folding stock with adjustable cheek piece, a new adjustable pistol grip and a new adjustable bipod.[9] Fitted with Hensoldt optic.[10] No longer in production.

SG 551

Shortened version of the SG 550 featuring the same length handguard but a 14.3 in (36 cm) barrel and a shorter gas tube and gas piston. Numerous variants of the SG 551 exist:

  • SG 551-1P: Police carbine version. Features a Hensoldt optic and a detachable cheek riser.[11]
  • SG 551 SWAT: Features corrosion-resistant finish and optical sight mount.[4]
  • SG 551 LB: Features extended 17.9 in (45 cm) barrel. Can mount underbarrel grenade launchers or bayonets.[12]
SG 552 Commando

Officially known as the SG 552-2P,[13] introduced in July 1998. Features a shorter barrel, shorter overall profile and redesigned action. Discontinued in 2008 and replaced by the SG 553. Upgrade kits available to convert an SG 552 into an SG 553. Variants of the SG 552 exist:

  • SG 552 LB: Features longer 13.6 in (35 cm) barrel.
  • SG 552-A1: SG 552 converted to SG 553 standard. Features new bolt carrier, charging handle, recoil spring and gas tube.
SG 553

Improved version of the SG 552. Resembles the SG 552 in many aspects but features an improved action where the recoil spring is wrapped around the piston rod; this helps address various reliability issues found on the SG 552. Also known as the Stgw 04.[14] Variants of the SG 553 exist:

Civilian[]

SG 550 VRB

Pump-action version intended for areas with stricter firearms laws. Noted as being unsuccessful with only 12 produced.[20]

SIG 556

Semi-automatic version of the SG 550 series partially made in the United States due to import restrictions. Discontinued as of May 2017.[21] Manufactured by SIG Sauer Inc. in New Hampshire. Numerous variants exist:

  • SIG 556 Classic: Features slimmer profile handguards and hooded front sight.[22]
  • SIG 556 DMR: Features match-grade trigger and barrel and various other improvements.[23]
  • SIG 556R: Version chambered for 7.62×39mm.[24] Early production runs had some issues resolved on later versions.
  • P556: Stockless carbine version.[25]
SIG 556xi

Highly enhanced and modernized version of the SIG 556. Noted as being fully ambidextrous and caliber-convertible.[26] Discontinued as of May 2017. Variants exist:

  • SIG 556xi Russian: Version chambered for 7.62×39mm.[27]
SIG 522LR

Sub-caliber sporting rifle version styled after the SG 551. Uses blowback and as such has no parts commonality with other versions of the SG 550 family.[28] Discontinued as of March 2017.

Related weapons[]

SG 750 and 751

Battle rifle versions of the SG 550 family.[29]

Gallery[]

References[]

  1. https://patents.google.com/patent/US4433611A/en?oq=US4433611
  2. https://modernfirearms.net/en/assault-rifles/switzerland-assault-rifles/sig-550-551-552-556-556xi-eng/
  3. https://www.militaryfactory.com/smallarms/detail.asp?smallarms_id=616
  4. 4.0 4.1 http://www.sigsauer.swiss/en/sg-551-swat-assault-rifle.php
  5. 5.0 5.1 5.2 5.3 http://pdf.textfiles.com/manuals/FIREARMS/sig_550_551.pdf
  6. https://web.archive.org/web/20070822151929/http://www.biggerhammer.net/sigamt/kern/
  7. https://www.tapatalk.com/groups/theswissriflesdotcommessageboard/nato-bayonet-for-the-sg-55x-t7023.html
  8. https://www.proxibid.com/Firearms-Military-Artifacts/Firearms/Scarce-SIG-SG-550-1-Semi-Automatic-Sniper-Rifle-with-Scope-Case/lotInformation/44694864
  9. https://remtek.com/arms/sig/sniper/550snip.htm
  10. https://www.forgottenweapons.com/sig-550-1-sniper-answering-a-question-nobody-asked/
  11. https://remtek.com/arms/sig/551/551p.htm
  12. http://www.sigsauer.swiss/media/files/catalog-2018.pdf
  13. http://www.defensereview.com/sig-552-commando-mini-assault-rifle-for-special-operations/
  14. http://www.sigsauer.swiss/en/sg-553-assault-rifle.php
  15. http://www.sigsauer.swiss/en/sg-553-al-ch-assault-rifle.php
  16. http://www.gunsite.co.za/content/gunsgear/swiss-arms-sig-sg-553-sow-commando/
  17. http://www.sigsauer.swiss/en/sg-553-bk-assault-rifle.php
  18. http://www.sigsauer.swiss/en/sg-553-r-assault-rifle.php
  19. http://www.sigsauer.swiss/en/sg-553-al-us-assault-rifle.php
  20. https://youtu.be/pPq1WweDIK0
  21. http://sigforum.com/eve/forums/a/tpc/f/630601935/m/6790011464
  22. https://www.the-armory.com/shopsite_sc/store/html/product1847.html
  23. https://www.the-armory.com/shopsite_sc/store/html/product1418.html
  24. https://sofrep.com/gear/sig-sauer-556r-russian/
  25. https://www.thetruthaboutguns.com/gun-review-the-sig-sauer-p556-pistol/
  26. https://www.tactical-life.com/firearms/sig-sauers-556xi-boasts-best-ak-ar/
  27. https://www.thetruthaboutguns.com/gun-review-sig-sauer-556xi-russian/
  28. https://www.gunmart.net/gun-reviews/firearms/rifles/sig-522
  29. http://www.sigsauer.swiss/en/sg-751-precision-rifle.php
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