A counterweight for the Nomad head harness. The empty pod weighs 4oz, and 10 rounds of 5.56 (.223) comes in at another 4oz, yielding 8oz of counterweight in a sleek package.
Stainless steel 'dummy' rounds are available as a separate item, and those are 2x the weight of a standard 5.56 round (yielding 12oz counterweight).