how would you balance it then?
Simple, it balances itself as it is.
-It does more damage then the Handcannon, to the point of one-shotting crawlers on HoE easily.
-Slow rate of fire (you can really spam this thing nilly-willy like the other pistols/revolver, slower then the other pistols, but not too slow to the point each act like a damn rifle)
- decent recoil (basically that of the Magnum or so)
-small ammunition size (5 round cylinder, so when dualwielding, you're only getting 10 shots out there, so this forces to the player to be a bit careful with it)
-accuracy should be high actually.
-with a 12 weight system when holding 2 of them, it pretty much swallows your entire inventory (1+12=13/15, thus allowing you to only hold a Machete and pipe bombs), even at 5.5 (for Gunslinger perk if it ever gets a chance to be on the basic game), you would still be unable to grab anything else but the weapons I listed, or a Katana (5.5x2=11+1=12/15, 3 spaces leftover).
-Price for gun itself will of course be higher then Handcannons totally (2,000 in base price perhaps), while the ammunition is actually expensive somewhat (bullets specifically designed for the revolver? Yeah, expensive).
Overall this would and should balance the weapon quite nicely for both sharpshooter and Dualwielding Gunslingers.