AAP-01 Short stroke kit, including a Hadron Designs specific 300% upgraded spring.
 
Hadron tested 150, 200, 230% variation springs with most leading buckings.. But our 300% gave 100% feeding consistency in most SS (shortstroke) applications. 
 
The shortstroke segment, is made from a bouncy material, effectivley taking the impact of the bolt, and bouncing it back. Hence why we nickname this kit, the "Bouncer".
 
This material property lessens the shock to the rear sight assembly.
 
Please note, there is a small solid tube as part of the segment, which is removed before fitting into the rear spring assembly. This small solid tube, and inserted into one end of the nozzle return spring, as per pictures. This is optional.
 
This provides a stiffening guide and tiny bumper for the nozzle spring assembly, when under full compression.
 
As used by numerous YouTube airsofters across the globe.
 
Install, and welcome to the BRRRTTT.