Magneto Pistol Sniper (base damage 20-35) with...
5.10.4.1.6.10.9 with One-Handed/Bruiser and:
MCrits@3, EMCrits@6, SharpS@9, BCrits@12, RBtEyes@15, BRoFire@18, ABoy@21, ABoy@24
He only needs cola and ends with 262% Energy Weapons skill, 10 Action Points, fires 3 times per turn.
(You could swap Bruiser with Small Frame but you still won't get another shot per turn and you'll need Buffout)
***OR***
Maybe a .223 pistol sniper (base damage 25-35) with...
5.10.4.1.6.10.9 with One-Handed/Bruiser and:
MCrits@3, EMCrits@6, SharpS@9, BCrits@12, RBtEyes@15, BRoFire@18, ABoy@21, ABoy@24
He only needs cola and ends with 265% Small Guns skill, 10 Action Points, fires twice per turn.