This upgrade kit is for the ASG ASW338LM and licensed McMillan M40A3 spring sniper rifles. This kit includes the all metal Zero-Trigger assembly and a full metal M150 spring cylinder set. The Zero Trigger vastly improves trigger performance by using high strength metal parts that make the trigger pull very smooth as well. The M150 cylinder set has a stainless steel cylinder, brass cylinder head, piston, M150 spring and spring-guide. Assembly is incredibly easy and takes less than 5 minutes to install.