Claim this seasonal Strand rocket launcher while you can.
Crowning Duologue is one of only two Strand rocket launchers in Destiny 2, the other being Semiotician from last year's Season of the Witch. Since The Final Shape released, however, that weapon has become a lot harder to get, leaving you with few options if you're a new player looking for a Strand rocket launcher.
Crowning Duologue is also a Solstice weapon, meaning it's only available as part of this year's event. The good news, though, is that it received a perk rework alongside the other event weapons. This rocket launcher can now get Bait and Switch plus Reconstruction, a perk combo that makes it a competitive choice alongside some of the best RLs in the game like Apex Predator and Crux Termination IV.
One of the nice things about precision frame rocket launchers is also that they automatically lock onto enemies you aim at, as with the Tracking Module perk. Here's my favourite Crowning Duologue god roll for PvE with its new perks, plus a roll you can use in PvP if you want to bring a Strand rocket launcher for whatever reason.
If you plan to use Crowning Duologue in PvE for damaging tough enemies and bosses, then it has a number of decent DPS rolls. If you're looking for pure damage, then Reconstruction plus Bait and Switch is your best bet. The first is essentially a better version of Auto-Loading Holster that will reload your rocket launcher up to two rockets, while Bait and Switch is still among the best damage perks in the game, offering a 30% buff for ten seconds upon dealing damage with your other two weapons.
If you'd prefer more rockets, then you could swap out Bait and Switch for Envious Assassin, or even Bipod, though beware that even though the latter increases mag capacity by one and reserves by five, it reduces damage by 25% as well as nerfing your reload speed. Reconstruction and Bipod would mean four loaded rockets, since Bipod buffs mag size and Reconstruction reloads double that, but that 25% loss is usually a deal breaker for most.
Lastly, I'd recommend Alloy Casing for faster reload speed, plus a reload speed masterwork, if you are going to be manually reloading during a DPS phase rather than doing a rotation of multiple weapons and allowing Reconstruction to do the work. Otherwise, a velocity masterwork will get your rockets onto their target quicker, pairing nicely with the intrinsic tracking to help hit bosses with squirrely movement. As for barrels, don't sweat it too much, but Smart Drift Control, Linear Compensator, or Quick Launch are recommended.
Though grenade launchers or machine guns are a bit more efficient in PvP, if you decide to bring a Strand rocket launcher for whatever reason, Crowning Duologue does have a few decent perks. I'd personally recommend Impulse Amplifier and Cluster Bomb. The first perk massively boosts velocity, making it more likely your rocket actually hits who you're firing it at, while the second creates small explosions around the initial blast, making it more likely you'll catch someone, too. Chain Reaction might also help with collaterals, although honestly if a teammate is standing close enough to get tagged they're probably dead already.
For the Launcher Barrel, Volatile Launch will buff blast radius to the benefit of Cluster Bomb, while High-Velocity Rounds will increase projectile speed even further. The precision frame's inherent tracking might come in handy in certain PvP situations, but if your opponent is evading behind cover, it's more likely the rocket will track into a wall, so hip firing with it will generally be your best bet.
