The STGW57 was the standard issued rifle for the Swiss Military Service from 1957 to 1990. It is a select fire rifle chambered in the same cartridge as this rifles predecessor, the K31. The SIG SG510 was chambered in 7.62×51. Along with sharing the same cartridge as the K31, you will notice the STGW57 has a similar T-shaped charging handle on the right side of the receiver.
Interestingly the STGW57 also had flip up iron sights.
For more information on the STGW57 check out this rather indepth look at the rifle on YouTube.