In the Buy Menu, the description for the Bucky's Alternate Fire (Right Click) states that the "Canister does no damage until it detonates".

This is actually incorrect, if an enemy is hit by the Canister itself, they take 15 damage from legshot, 20 damage from body shot, and 40 from a headshot which makes it stronger than the judge when you completely whiff but one pellet hits the head.

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https://reddit.com/link/krd3f8/video/w6idenr97m961/player