SIG SG 530

Development

In 1963, SIG and Beretta began working together on a new rifle. They wanted something modern, light, and affordable that fired the 5.56x45mm NATO round. The two companies had already teamed up to produce the SG 510-4 for Chile.

The SG 530 was built from stamped sheet steel with hardwood furniture. It kept the roller delayed-blowback system from the SG 510 for controlled unlocking, but making that system work with the 5.56mm cartridge caused problems. The round's higher velocity led to extraction issues, and there was a greater risk of ammunition cooking off in a hot chamber. To fix this, the roller-lock mechanism was combined with a long-stroke gas piston.

This makes the SG 530 unusual: it is both gas operated and roller-locked. When the rifle fires, propellant gases are tapped from a port in the barrel and sent into a gas cylinder. There, they push on a piston head attached to the bolt carrier.

That force drives the carrier backward, and a cam on the carrier rotates the bolt head to unlock it, camming the rollers inward to extract the spent cartridge. This hybrid setup also made the rifle easier to control, since the gas pressure managed bolt movement better than the original delayed-blowback design. The SG 530 took a lot of inspiration from the Heckler & Koch G3 and the Spanish CETME Model 58, especially in placing the charging handle on a gas cylinder mounted above the barrel. That gas cylinder also houses the long-stroke gas piston and the recoil spring, and it keeps the chamber away from residual heat to stop rounds from igniting too early.

In 1968, Beretta stopped working with SIG and started developing its own 5.56mm rifle. SIG continued alone on the 530. Beretta released the AR70 in 1972, which looked similar but had key differences: the charging handle moved to the right side of the bolt carrier, and the bolt became a rotating type, like the one on an AK.