It is sold by Arms Dealer.
Shotgun sits in the Early Hardmode tier of Terraria progression based on its rarity rating (4).
Unreal is the strongest prefix for Shotgun — +15% damage, +10% speed, +10% crit, +15% knockback (ranged only).
Shotgun deals 24 base damage, 45-tick use time. Use the DPS calculator to see expected damage per second with prefixes and crit applied.
Shotgun is used as an ingredient in 1 recipe. See the "Used to craft" section above for the full list.