ATK said the follow-on delivery order comes two weeks after the initial contract was announced.
Work for the second order will be performed in Eagle Industries' Puerto Rico manufacturing plants and is expected to be complete Jan. 31, 2013.
The two contracts together are valued at $75 million.
"The new USMC pack system provides Marines with a simple and effective load-carriage system that can easily be customized to support their mission, with or without body armor," said ATK Security and Sporting group President Ron Johnson. "We are honored to have been selected as a key supplier of this mission-critical product and proud of our role in supporting the Marines."
The new load-bearing equipment system is designed to allow Marines to carry equipment needed in support of combat operations. ATK said its system maximizes the ability to carry combat loads more efficiently, minimizes the burdens of weight and improves overall system compatibility.