Heavy Weapon Harness (5e Equipment)
From D&D Wiki
Weight: 15 lb.
A heavy weapon harness is a strap-on harness with a chest plate on the front. Mounted on the chest plate is an articulated, double-jointed hydraulic gripper which is capable of suspending or bracing heavy weapons as well as a bipod or tripod - the only difference being the harness is much more mobile. The harness can be adjusted to be worn over armor.
While you are wearing a heavy weapon harness, firearms which are normally mounted or otherwise impede your movement such as heavy machine guns and heavy flamers do not restrict your movement. Additionally, you can wield a single firearm as if you were one size category larger than your actual size. The harness' gripper does not count for any reason count as an additional hand, or arm, as it is only designed to support firearms, not aim or fire.