Generally speaking, there are two classes of rubbers - hard and soft. The general rule-of-thumb is to use a soft rubber if you're rifle's velocity is under 400 fps, and a hard rubber for velocities over 400 fps. Some manufacturers provide a number, while other are just colour coded for hardness/softness.
VFC SCAR-L - VFC SCAR SSR - KJW Hi-Capa 5.1 - CAW M79
The Three Sisters - WE G39 E/K/C
Originally Posted by kalnaren
Stalker stays where he is.
His BB's fly across the country to hit their target.