[Snake]

Lolzy is right. But all we can do here is to buff other classes that do use guns, in order to balance it. Like for example Demon Hunter's Desperado Stance. (In which I already pleaded for changes in one of those million Balance Fu threads down there.) Or Engineer. But all I can do is sigh here and expect nothing to go wrong after this buff/purposal.
There are a few handguns that worry me if they sudden get +30 Critical Hit out of nowere, such as Ryeser. Which it's only two counterplays are to not be critically hit or pack lightning resistance, although Null Shell takes care of it as stated by Fern, once again looping back to what Lolzy said. Magic Gunner is the thing that fucks everything up. S i g h.

So, let me just repeat my proposal with minor tweaks. How about this:

Keyshot
Ideally, one shot, one kill. Aiming for vital points helps too. It's all about hitting that key shot. Increases Critical Hit when using Bows/Guns by X (X = Rank * 5). For guns, it only affects the first shot made.

Rank 1: +5 Critical Hit (Bow/Guns only)
Rank 2: +5 Critical Hit (Bow/Guns only)
Rank 3: +5 Critical Hit (Bow/Guns only)