History of Arms Week Engram

Arms Week Engram is a reward from Arms Week, a one-week event built around a single weapon archetype. Engrams cost 25 Combat Telemetry each. Telemetry is turned in with Ada-1 in the Shooting Range in the Tower, who also gives the Initial Calibration quest.

Arms Week is no longer running. Shattered Vault lists the content as legacy, and TheGamer notes that Arms Week is declared at certain points in a season.