The GSI 3S Steel Buffer improves the load time, high threshold, and stable operation for VFC HK417 / G28 GBBR thanks to the weight of the steel buffer.
While increasing the load time, the continuous shooting speed is maintained, and maximizing gas power is expected.
Internal tension structure increases sensitivity compared to spherical shape and lowers surging noise. (the original is structured as external tension, which makes loud noises).
MC-Engineering Plastic-Material Buffer Endings are shock-resistant and provide upgraded weight.
Consists of two springs with different elasticities for seasonal use (cold, warm, and hot weather variations) or for setting your preferential speed for shooting.  
Lowering surging noise thanks to the “D” cut makes it easy to disassemble the unit and ensures a better airflow within the structure that it needs. 
The GSI’s 3S is a unique convention from its own engineering efforts to improve airsoft gun operation: 
Silent – decrease the noise 
Smooth – Improve seamless operation 
Shockup – Load time will be dramatically increased