"Gun made from a trumpet. What'll they think of next?"
— In-game description
The Trumpet Gun is a ranged weapon which is the Classic Gun's evolution. This gun looks like a trumpet with a wooden grip. It's a low tier weapon (Tier 2) : it will gain 3 Synthesis Points (SP) when it gains a level. It has no special abilities. Like his predecessor, it is a semi-automatic gun which is effective against airborne enemies, but against armoured enemies, a wrench or a beam gun is more effective.
You can buy it from Gerald when he joins your party, you can invent it, or you can find it in treasures chests in Dungeons. But eventually, you'll get one from Gerald, when you have to fulfill his quest in order to get him in your party.
When the Trumpet Gun is bought, found or obtained, as a Tier 2 weapon, it should have 42 Weapon Hit Points (WHP), like the Drill Wrench or the Turtle Shell Hammer for example, but instead of this, it has only 32 WHP, which is less than a Tier 1 weapon which has 36 WHP.