So I had an idea for a "magical gun slinger".
First, take artillerist, for the eldritch cannon. It can be tiny, and "Tiny one can be held in one hand.". Now you could continue with artillerist and use "arcane firearm" as your other "magic gun" and have fun with that. It's a valid charac ter.
But if you really want to pew pew pew... your character then finds an ancient weapon... perhaps cursed, or perhaps from an ancient but advanced civilization (or both). In other words, multiclass into warlock. So you start using Eldritch blast and the eldritch cannon. At level 5 you are looking at a very respectable 2d8+2d10+6 dmg, +8 at level 6 once you get your first ASI, and if you start using things like hex, summoned monsters etc your damage goes up even more.
"but this is MAD!" you say. Not really. See, the Eldrich cannon tells you to make a spell attack. it doesn't specify it has to be int based, you aren't casting a spell! So you can focus on charisma.
Is this a super powerful build? I think it's ok. But it seems like a very fun and flavorful one. I hope you have fun with it!