SIG SG 530

The SIG SG 530 was a prototype Swiss assault rifle developed in the 1960s by Schweizerische Industrie Gesellschaft (SIG) and Fabbrica d'Armi Pietro Beretta to take the then-new M193 ball and M196 tracer 5.56x45mm NATO military rounds. The 530 was only ever manufactured in small numbers, but was the basis for later, more successful projects, like the SG 540 and SG 550 rifles, as well as the Beretta AR-70.

Development

Development of the rifle started in 1963 as a joint project between SIG and Beretta to create a modern, light, and affordable rifle chambered in 5.56×45mm NATO. Beretta had already cooperated with SIG on the production of the SG 510-4 rifle for Chile. The SIG SG 530 was constructed primarily out of stamped sheet steel and hardwood furniture. The roller delayed-blowback operating system of the SIG SG 510 was retained for controlled unlocking, but adapting this mechanism for the 5.56 mm cartridge proved difficult: the rifle had extraction difficulties due to the round's higher velocity and there was a higher potential for ammunition cook-off in overheated chambers. To solve these problems, it was decided that the roller-lock mechanism would be paired with a long-stroke gas piston.

The SG 530 is arguably unique as a rifle that is both gas operated and roller-locked. After firing, the 530 is designed to tap propellant gases from a port in the barrel and directed into the gas cylinder, where they impinge on the piston head attached to the bolt carrier. This force drives the carrier rearward, with a cam on the carrier rotating the bolt head to unlock and cam the rollers inward, extracting the cartridge. This hybrid configuration also improved controllability by leveraging gas pressure to manage bolt movement more effectively than the original delayed-blowback setup.