The SIG AM55 is a prototype Swiss battle rifle.
The AM55 was the first successful rifle design made by SIG. borrowed heavily from other German World War II designs that were tried and tested. It used a delayed blowback, similar to the one in the MG 42. It was equipped with a wooden forearm and handguard, and a metal framed buttstock with wood inserts. The design of the AM55 was altered after successful testing, with a metal barrel jacket and rubber buttstock added. It was in this form that it was accepted for service as the Stgw. 57.
The AM55 borrowed heavily from most German World War II weapon designs, such as a delayed blowback similar to that of the MG 42's.