Century Arms VSKA Tactical The VSKA rifle features a bolt carrier, front trunnion and feed ramp machined from S7 tool steel and specially heat treated for maximum durability. S7 tool steel provides maximum shock resistance and high compression strength while retaining toughness. The VSKA incorporates a front trunnion and bolt that are machined from billet, a carburized 4140 steel bolt, a chrome-moly 4150 barrel, durable manganese-phosphate finish and RAK-1 Enhanced Trigger Group for an impressive trigger pull.