This piston assembly has been careful assembled by technicians here at Umbrella Armory. The piston is a SHS 14T piston. We hardness test every single piston rack to ensure they are passing our rigorous QC standards. The piston head is a Lonex POM piston head. We have never had an issue with this piston head. It is used in every single one of our builds. We use one metal washer behind the piston head to correct the angle of engagement and the third tooth has been shaved down to a 45 degree angle. This Piston Assembly is seen primarily in our Carbine and DMR type SSG builds.