Airsoftjunkiez demonstrate a custom HPA rifle build using an old Dytac Warlord that is equipped with a PolarStar F2 with UGS CO2 Insert 33g... "Polarstar CO2 inserts are manufactured for both the UGS and CGS stocks and have models for both the 12g and 33g CO2 cartridges in either variant. However, the inserts have more uses than just being paired with one of these stocks.