My build for the [Kuva Zarr]. Swap out [Rime Rounds] for [Primed Cryo Rounds] if you want against low level content. I recommend running a [Furax] with [Amalgam Furax Body Count] for maximum aoe. This build can work for barrage, but it is mainly designed for cannon mode. The option slot here is probably [Serration] if you have a maxed merciless. You can swap it for [Primed Fast Hands] if the reload is too annoying.

Synergies: Best frame synergy is definitely [Gauss], since he gives tons of reload, fire rate and stagger immunity. Here is my [Gauss] build (shameless self plug): https://overframe.gg/build/285497/
Energized Munitons is also crazy good with this weapon, even more so with Gauss. Combined, you can shoot a ridiculous amount of canonballs compared to a no-buff build.

I recommend Kuva Bramma if you don't want to use Energized Munitions and/or frame buffs, but the [Zarr] with all these bonuses is arguably better.

Finally, I recommend using a macro on pc to automatically click very fast, since it is quite hard to fire fast enough yourself.