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Borderlands 4 ARC-TAN Review — Legendary Shotgun

Published: 8/15/2026 · Updated: 11/14/2026 · As of 2026-07

Red Text
Not to go off on a tangent...

This review was machine-translated from the Japanese original. Numbers are checked against the original; if the wording reads oddly, the Japanese version is authoritative.

Even though it’s a shotgun, it fires grenades. A Torg-made “explosion-spreading” single. It fires grenades in a 2‑round burst instead of bullets, and upon impact they explode with a large area. At close‑to‑medium range it blows away groups with an explosion‑focused unconventional shotgun.

🧩 Origin of the red text Name ARC-TAN is a play on the trigonometric function arctan (arc tangent = inverse tangent). The red text “Not to go off on a tangent…” is a reference to the English idiom “go off on a tangent” and also a double meaning with the mathematical tangent (tangent) (Borderlands Wiki also mentions this mathematical wordplay). The grenade’s arcing flight also matches “arc”. There is no specific external citation (wordplay / self‑reference).

What kind of shotgun? (Beginner’s perspective)

• Torg-made shotgun. Fires grenades in a 2‑round burst instead of bullets
• Grenades explode on impact, involving a large area (splash) = strong for crowd control
• Torg’s signature explosion focus. Works well with builds that extend splash damage / area damage

Unique effects (mechanics)

KA-BOOM: Fires grenades in a 2‑round burst, and on impact they explode with a large splash radius.

• In‑game: KA-BOOM — Fires grenades
• Web (Lootlemon): KA-BOOM - The ARC-TAN fires grenades in a 2-round burst that explode on impact with a large splash radius.
• There are six possible elemental types (Kinetic/Fire/Shock/Corrosive/Cryo/Radiation) (Lootlemon). The previous listing “Fire” is just an example of an instance and not a fixed element (unverified)
• Quirk: Grenade launch has a lag until impact, so at very close range there is a self‑destruct risk. Use at a distance

Manufacturer part compatibility (license)

• Specific compatible license parts (unverified)

Drop & farming

Build compatibility

Summary

• Fires grenades in a 2‑round burst Torg-made explosive shotgun (KA-BOOM)
• Large area explosion on impact = excels at crowd control / area damage
• Obtained via Bounty Pack 2 (Stone Demon) Vault Card reward (DLC)

Related

• Same category (Shotgun): Anarchy / Bod / Acey May
• References: Lootlemon - ARC-TAN / MentalMars - ARC-TAN