This is the cotton bandoleer for the M79 rounds, it has 3 pockets on each end and has plastic "egg cups" that hold the round in place. Earlier versions had lower cups that didn't hold the rounds securely. The bandoleer wasn't a robust solution for carrying rounds into the field so this led to the development of the M79 vest, the early mesh version of which arrived in small numbers in 1967.

Pictures show that John "Tilt" Meyer used these bandoleers during range training with his cut down M79 Grenade Launcher.