Difference between 20mm rails and 30mm rails?
Hey everyone quick newbie question. What is the difference of 20mm rails and 30mm rails. I measured my barrel and it was around 20mm but what I am trying to find out is that. If the 20mm and 30mm are only lengths? Then why when you buy say a scope ring or somesort of attachment they are fit for say 20mm rails, 25mm rails and 30mm rails? If it was only length wouldnt they all be the same to fit rails in general?