Don't use the [Basmu] without a Riven Mod to give at least 45% crit chance

what the subtitle says. dont bother using the Basmu for anything other than priming if you dont have such a riven mod. in fact even with a riven mod, this thing isn't really good on Steel Path.

even though the radial attack is only 1.7 meters, which can be increased slightly with Primed Firestorm, it's fine considering how fast the fire rate is and with how many projectiles come out of this thing.

speaking of fire rate, there's no fire rate mod because i personally find the [Basmu] uncomfortable to use with a higher fire rate.

Rime Rounds is rank 0 to lower the weighing of viral as much as possible so elec and heat can shine more. a max rank [Rime Rounds] is fine though.

Faction variants

remember to use faction mods for big damage. should replace [Serration].
only use Rifle Elementalist for builds utilizing DoT (Damge Over Time). [Basmu] is a weird case which utilizes DoT but also raw damage, as in continually shooting at targets.
depending on the faction, you may want to add more formas like a vazarin polarity or even be forced to get another [Basmu] to be able to build for said faction. whhich is not worth it IMO.
if armor stripping, you can drop Hunter Munitions for Hammer Shot for more crit dmg or [Serration] if you use a faction mod for more dmg or Vigilante Armaments for more multishot.
note that you will most likely be having 2 element damage types for each faction.

Corpus

to get toxin, you have to also make radiation. at best, you will have an equal weighing between the two.

Corrupted

either raw viral if youre armor stripping or just the build as is on here.

Grineer

raw corrosive if youre armor stripping or just the build as is on here.

(Deimos) Infested

for regular infested, heat is best.
if you go with heat, you'll also have corrosive alongside it. other options are blast or gas. for gas you can still do raw dmg or high status chance.

for deimos infested, Blast or Gas, raw damage or utilizing high status chance is up to you.
you can also do corrosive alongside blast or simply do corrosive like with the grineer, but blast and gas are better.

Murmur

build for radiation, raw damage. best used with armor strip.