Quote Originally Posted by Turnup View Post
I think my understanding is rather better than yours.

That's not what it says. To be S5 an air pistol must be both over 6 fpe and fail one or both parts of the 300/600 rule.
No, because then it would say a barrel under 300 AND is less than 600 overall, it says "either or" so if it passes one of them it's good but still not an air pistol.