All the outfitted parts in Elite: Dangerous have a level and a class, broadly describing their performance.
So you have size 1 (small), 2 (medium) and so on for size ratings and A, B, C etc for class ratings (A being best but super expensive). Size counts more than class, so a 2-anything will be better than a 1 anything, and an A2 will be better than a B2.
Where can I find high class weapons?
I'm currently in an Eagle with 3 small mounts - shouldn't I be able to mount 3 A1 guns eventually (when I can afford them)? The problem is that (even in high tech systems) I haven't seen any size 1 guns better rated than F.
In particular is like to find gimballed size one guns better than a G rating.