The PSG1 differs from all normal AEGs. It puts the spring under tension at the end of the cycle. So at the very moment you pull the trigger a BB comes out. On normal AEGs the piston is all the way forward after a cycle. So if you pull the trigger on semi, the piston has to move all the way back which takes some precious time between the trigger pull and the actual shoot. However you can easily ease the spring by firing the gun in semi.
As it is not possible on PSG, you need to release the spring manually. As the M14 lacks the semi, that tool is the only way to release the spring. The other w