Which riffle on which SIG SG 550 is based is a 5.56×45mm NATO assault rifle developed in the early 1970s by Schweizerische Industrie Gesellschaft?
The SG 540
SIG SG 550
The SG 550 is an assault rifle manufactured by Swiss Arms AG (formerly a division of Schweizerische Industrie Gesellschaft now known as Sig Holding AG) of Neuhausen, Switzerland.
 "SG" is an abbreviation for "Sturmgewehr", or "assault rifle".
 The rifle is based on the earlier 5.56mm SG 540 and is also known as the Fass 90 ("Fusil d'assaut" 90/"Fucile d'assalto" 90) in French/Italian or Stgw 90 in German ("Sturmgewehr" 90).
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SIG SG 540
The SG 540 is a 5.56×45mm NATO assault rifle developed in the early 1970s by Schweizerische Industrie Gesellschaft (SIG, currently SAN Swiss Arms AG) based out of Neuhausen, Switzerland as a private venture primarily destined for export markets and as a potential replacement for the 7.5×55mm Swiss SG 510 automatic rifle known as the Stgw 57 in Swiss service.
Beta C-Mag
The Beta C-Mag is a 100-round capacity drum magazine manufactured by the Beta Company.
 It was designed by Jim Sullivan and first patented in 1987 and has been adapted for use in numerous firearms firing the 5.56×45mm NATO, 7.62×51mm NATO, and 9×19mm Parabellum cartridges.
 "C-Mag" is short for "century magazine", referring to its hundred-round capacity.
 It has two drum units, each of which hold half of the cartridges inserted into the magazine.
 The latest version of the magazine is available with a transparent backing to allow the user to see the number of rounds remaining in the magazine.
 A C-Mag loaded with 5.56×45mm NATO ammunition typically weighs about 2.1 kg ; a C-Mag loaded with 7.62×51mm NATO ammunition weighs 4.77 kg . S&amp;T Daewoo XK8
S&T Daewoo XK8, also known as DAR-21 (Daewoo Assault Rifle-21st Century), is a 5.56×45mm NATO bullpup assault rifle developed and manufactured by S&T Daewoo intended to replace Daewoo Precision Industries K2 assault rifle for the Republic of Korea Armed Forces.
 XK8 was the first firearm developed solely by the Korean defense company without the request from the military.
 However, after the field tests by Republic of Korea Army Special Warfare Command, it was rejected and was not mass-produced.
 The rifle is now offered for export only. SIG SG 530
The SIG SG 530 was a Swiss assault rifle developed in the 1960s by Schweizerische Industrie Gesellschaft (SIG) to take the then-new 5.56×45mm NATO round.
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The Model L is a Spanish 5.56×45mm NATO assault rifle developed in the late 1970s at the state-owned small arms research and development establishment CETME ("Centro de Estudios Técnicos de Materiales Especiales") located in Madrid.
 The rifle retains many of the proven design elements the institute had used previously in its CETME Model 58 battle rifles. Zastava M90
The Zastava M90 was an assault rifle developed and produced by Zastava Arms in SR Serbia, SFR Yugoslavia.
 It was developed from the famous Zastava M70 assault rifle, the modified copy of the Soviet AKM assault rifle, but with a Western type flash eliminator added on the barrel end, chambered in also Western, 5.56×45mm NATO caliber, and with that a different magazine design, similar to Western STANAG magazine AK-101
The AK-101 is an assault rifle of the Kalashnikov series.
 The AK-101 is designed for the world export market, using 5.56×45mm NATO cartridges, which is the standard of most NATO armies.
 The AK-101 is marketed at those looking for a weapon that combines the logistical compatibility and familiarity of the 5.56×45mm NATO round with the reliability of a Kalashnikov.
 It is designed with modern and composite materials, including plastics that reduce weight and improve accuracy.
 Many of the improvements found in the AK-101 are also present in the AK-103 and the rest of the AK-100 series of rifles. Heckler &amp; Koch G41
The G41 is a German 5.56×45mm NATO assault rifle introduced in 1981 and produced in limited quantities by Heckler & Koch.
 It was designed to replace the 5.56mm Heckler & Koch HK33 in service providing a more modern weapon compatible with contemporary NATO standards.
 It is chambered for the 5.56×45mm NATO cartridge and can use both SS109 and M193 ammunition.
 Assembly of the G41 has been discontinued by Heckler & Koch, however, production rights to the rifle were acquired by the Italian arms manufacturer Luigi Franchi. Intermediate cartridge
An intermediate cartridge is a rifle/carbine cartridge that is less powerful than typical full-power battle rifle cartridges, such as the .303 British, 7.62×54mmR, 7.92×57mm Mauser, .30-06 Springfield or 7.62×51mm NATO, but still has significantly longer effective range than pistol cartridges.
 As their recoil is significantly reduced compared to high power rifle cartridges, fully automatic rifles firing intermediate cartridges are relatively easy to control.
 However, even though less powerful than a traditional full-power rifle cartridge, the ballistics are still sufficient for an effective range of 250 – , which are the maximum typical engagement ranges in modern combat.
 This allowed for the development of the assault rifle, a selective fire weapon that is more compact and lighter than rifles that fire full power cartridges.
 The first intermediate cartridge to see widespread service was the German 7.92×33mm Kurz used in the StG 44.
 Other notable examples include the Soviet 7.62×39mm used in the AK-47 and AKM series, 5.45x39mm first used in the AK-74, and the American 5.56×45mm NATO cartridge first used in the M16.