This build for the [Rauta] is primarily designed to increase its combat efficiency, as well as reliably trigger Slash and Viral procs.

Faction Damage mods aren't really negotiable; with [Rauta]'s low base Crit Chance, you're not going to spike damage for powerful bleeds as well as hybrid weapons, so you'll have to rely on Slash procs double-dipping on Faction Damage multipliers to get the bulk of your damage.

Other Notes

• [Sweeping Serration] is used to more heavily weight the proc chance per status towards Slash, since that's going to be the bulk of this weapon's damage.

• Shotgun Barrage can be replaced with its Amalgam counterpart to no detriment, if team utility is desired.

• Primary Dexterity is technically replaceable, however the Rauta's unique gimmick of increasing your Melee Combo Counter on-hit really encourages the use of melee weapons, and in that regard, Primary Dexterity's +7.5s Combo Duration is very welcome.

• If you have your Viral Priming bases covered, you could opt to switch out [Toxic Barrage] for [Scattering Inferno], giving the [Rauta] AoE burst damage potential through Blast Procs.

Use Cases

The [Rauta] exists in an interesting space due to how it encourages the use of melee weapons, which gives it some unique use cases where running it would be desirable;

• Melees with low base attack speed can have their combos stacked up faster, which can kickstart Berserker Fury where applicable.

• Heavy Attack focused builds can now get more convenient damage spikes without having to dawdle with weak light attacks or fuss around with bonus Combo Count mods.

It is worth noting, however, that the [Rauta] does not function properly with the [Venka Prime] at present; resetting the combo down to 12x even with [Venka Prime]'s 13x Max Combo Multiplier.

EDIT: As of update 35.1.0, the [Rauta] now properly stacks [Venka Prime]'s combo count upwards to 13x.

EDIT #2: [Seeking Fury] has been phased out of the build and replaced with Shotgun Elementalist.

EDIT #3: DE has announced a complete rework to Pseudo-Exalted Melees is coming in March with Techrot Encore. This may affect the Rauta's synergy with frames like Atlas, Khora, Gara, and Ash. If it does, I will update the guide/description here to reflect that.

EDIT #4: As of update 38.5, the Rauta's Combo Generation on-hit no longer affects Pseudo-Exalted Melees like [Khora]'s [Whipclaw], [Atlas]' [Landslide Fists], or [Ash]'s [Shadow Clones]. The extended combo duration from Primary Dexterity still takes effect, however.