[ILLusion]

I believe "Duracon" is Systema's name for a silicon type polycarbonate material.

"Polycarbonate" is simply the industrial term for "plastic".

I use both ball bearing spring guides and piston heads extensively, as do many other users. It relieves the twisting tension of the spring during it's compression stage. On top of that, the added height of it adds a higher preload to the spring. The result of these two forces leads to a higher velocity consistency, as well as a higher muzzle velocity.