-4 AP to fire chemical/energy guns
+5% THC with chemical/energy guns
-4 ap for energy is about equal to -3 for firearms because energy/chem are about 1/3 slower than firearm pistols: 22 vs 16 (fastest), 40 vs 32 (slowest). And i'm not taking rapid reloader into account.
AP reduction is a very good fit for those weapons because of how on-hit effects work and 4 out of 6 have them. Oh, and there are those unique pistols with on-hit effect as well.
Sure, someone who manages to max DEX would get some 'nice' numbers for some chemenergy pistols but i'd not say those numbers are too 'nice' because you can't max DEX without sacrificing something: you won't have all of Steadfast Aim, Sharpshooter, Practical Physicist/Mad Chemist. And since SA works well with Sharp and PP, and MC helps chemguns greatly at not sucking, you typically want all 3 (4).
+5% THC is to differentate it from Gunslinger, to balance it with Gunslinger and to give chemenergy what they need. Chemenergy not only have lower range than firearms, which affects THC, they also can't mount laser sight. Even laser pistol is less accurate than average firearm with laser sight. Another reason why accuracy is important for chemenergy is that they need to roll twice to do their job - first for hitting and then for their on-hit effect, so chances for on-hit effects are actually lower than item description states. Plasma pistol needs it badly as well since missing with it sucks as much as missing with sniper rifle and plasmas don't have innate accuracy bonus, huge optimal range nor ability to mount scope, like SRs do.
This feat is also a non-crafting feat and ... yeah, that's also what chemenergy need, since firearms have Rapid Fire, Gunslinger and Expertise.
Requirements are just what i felt would fit. DEX is there due to AP reduction, PER is there due to THC bonus, both are at 6 because both Point Shot and Steadfast Aim are like that.
Ditto for Guns 25.
I was thinking of "X electronics or X chemistry" requirement, as using those weapons without crafting is pretty mad (but not Mad Chemist!), but it does not quite fit a non-crafting feat.