This [Zarr] is built to be excellent and murdering liches, without investing so much into it to undermine its effectiveness at completing lich nodes in the process. We're building around multi-shot and critical for this, with elemental mods used to increase the damage per pellet.

Serration/Heavy Caliber aren't used for three reasons:

• Given we shoot the cannon into crowds, the elemental mods we have get multiplied by 4.6 from merciless, rather than simply added on top of the [Serration] benefits (both merciless and base damage mods stack additively, rather than multiplicatively like with elemental mods).
• We want as tight a spread as possible when we switch to barrage mode , so as many pellets hit the head of our lich when we aim at it. Headshot bonuses help spike the damage further, and as each pellet is accounted for independently in lich DR, all together it translates to very high damage per shot.
• The barrage mod fires so many pellets that it will likely max out any statuses on the gun in one shot, even without additional status; using the primed cold and basic toxin elemental mods makes this maxed status viral to further increase the damage-per-pellet (both for ourselves and our teammates).

We're also using Vigilante Armaments instead of other elemental/faction mods for the following reasons:

• Vigilante gives us more pellets, which means more damage that bypasses DR calculations on the lich
• It increases the set bonus of the Vigilante set, which means more boosted crits, which means more damage per-pellet. Given the ungodly amount of lead we're force feeding the lich, with this we're likely to see at least 5 boosted crits per barrage (one of which has a 50% chance of getting boosted into red-crit level).

Finally, [Primed Firestorm] + [Hunter Munitions] is added to allow us to fire indiscriminately into crowds and build up [Galvanized Chamber] and Primary Merciless. This does begin to fall off for rank 4 and 5 liches, in which case replacing [Firestorm] with (Primed) [Bane Of Grineer] would be worth considering; this does come at the cost of faster enemy clear on Defense, Survival, and Exterminate missions, though. Besides, rank 4 liches are, at worst, a 50-50 of occurring, and if you play your cards right rank 5 liches should not appear at all.

Some final notes regarding the weapon's elemental choice and potential synergies:

• Radiation was selected as it helps to ignore the armor on most grineer (excluding Kuva fort, which you really should not be seeing) while also slightly reducing the number of shots aimed in your direction when taking care of the lich. If you intend on using this to [Hunt] Sisters as well, magnetic would be worth considering instead. However, as long as it isn't toxin or cold (as both would reduce the elements available to support your Galvanized Aptitude teammates), this should work out well.
• Any ability which slows/immobilizes the lich is particularly valuable with this build, as it allows you to more easily line up headshots.
• Sevagoth is a particularly good pick with this build, as his Gloom and Embrace can make head-shots trivial to land, and Reap can multiply incoming damage from all of your teammates. One just needs to be careful to not be overwhelmed by the incoming damage, as he can be incredibly frail without support.
• Most Kavat/Vulvaphyla buffs can further aid in lich killing, either by occasionally making the crit damage truly nuclear (Smeeta/[Adarza Kavat]) or keeping themselves alive indefinitely without your supervision (Vulvaphylas).