The perk is exclusively on the epic variant for the R.A.W. Light Machine Gun known as the R.A.W. - Liberty. Said Gun Perk makes the gun have double(2x) the amount of ammo in its magazine at the cost of the player being unable to reload it.
It is recommended that the player is always aware of their ammo count in the gun because, as previously stated, the player is unable to reload the magazine.