Which archgun is the most like an RPG?

[SupremeMachine_V1]

Basically what the title says. I wanted to get the Morgha, but when I watched a video where someone used it, its projectiles travelled in an arc instead of what I imagined, where it shoots straight like a missile. Are there any archguns that are like what I’m wanting, or are there none?

[(PSN)slightconfuzzled]

Hmm unfortunately I don't really think there is a good candidate for what you are asking. The closest I can think of, isn't even an Arch Gun but the Kuva Ogris (which is described as a Rocket Launcher). Most of the others are either beam weapons, flame throwers, heavy machine guns, etc. Kuva Ayanga is explosive, but also has an arc, also wouldn't really describe it as an RPG. 

The Wikia page has brief descriptions of them and there aren't that many, if you wanted to double check. 

[RobWasHere]

Closest would be Grattler, its explosive and goes on straight like but its more of a flak gun than RPG.

Otherwise Larkspur secondary fire is an explosive projectile, but its kind of weak compared to the rest of the guns.