The UFA-S is precision swiss lathe turned & manufactured from certified 4140 Cr-Mo steel, giving improvements to strength, corrosion resistance and durability over the original materials. Parts are all heat treated to 48-52 Rc (Rockwell C). In addition all parts are QPQ (Quench Polish Quench) Nitrided for improved corrosion resistance and enhanced lifespan. The main Plunger spring is manufactured with the improvement of Stainless 316 music wire (as per ASTM A313) for enhanced corrosion resistance. Closed end coils are also used rather than the original open ends for improved seating and alignment. Springs are stress relieved and air cooled. The Plunger Detent Spring is improved and manufactured from Zinc plated music wire (as per ASTM A288) for enhanced corrosion resistance. Springs are all stress relieved as per the mil specification. The assembly is retained within the upper receiver with an improved spiral design pin as opposed to a slotted version for increased strength and durability. Pins are fully certified by the manufacturer. The design of the Cap has been improved by reducing its diameter and snagging potential, creating a more streamline surface flow when assembled into the upper receiver. Exterior surface knurling around the caps edge allows for positive engagement with a gloved or naked hand while removing the circular ridge that exists on the current design. Weight of the assembly has also been improved to 20.227g (.7135oz) from 22.481g (.7930oz). All outer details are bead blasted to create a satin, reduced reflectivity surface prior to finishing. Manufactured in the USA from USA sourced materials and finishes.