Adaptation from https://overframe.gg/build/220285/

Using the same concept of dual barrel (that old players are used to on Tigris) we min-max the single shot reload and can change the built for quite some flexibility with 5 formas, which is really rare for guns nowadays #blameDE
This build slashes bodies viably with [Sweeping Serration] so it's viable to farm along a [Nekros].

Let's look at pros and cons of some options:

Primed Faction Mod ([Primed Shotgun Ammo Mutation] r8)
27% to proc Bleed per pellet
Highest Bleed DoT
removes Heat damage for extra bleed (usually this is discarded without a thought but we now have Galvanized Savy)

[Blaze]
27% to proc Bleed per pellet
High Bleed DoT

[Scattering Inferno]
33,8% to proc Bleed per pellet
Lower Bleed DoT

I don't have the full build to crunch the numbers and playtest max Primary Merciless + [Galvanized Savvy] interactions with the rest on the Bleed DoT, so it's hard for me to pick one of these over the others. I'd say that if you aren't running another source of Heat just go with Blaze/[Scattering Inferno].
Keep Primed Shotgun Ammo Mutation at r8 to open up flexibility. If you like to shoot from a far you can swap it for Galvanized Acceleration.

Have fun

PS: I've noticed some builds from other people that discarded [Primed Point Blank] without much change on RAW DAMAGE. I personally don't feel at ease to do so and putting all my chips on double "On Kill" triggers making it harder for me to [Reach] higher damages while also sacrificing Bleed DoT.