Probably the variant rule that's in the DMG for missile fire going stray.
That said, whatever logic you want to apply to this, disintegrate does not, by the published rules in the PHB, destroy the armor of whoever the ray hits. The exception would be if they roll a one on their saving throw.
That said, whatever logic you want to apply to this, disintegrate does not, by the published rules in the PHB, destroy the armor of whoever the ray hits. The exception would be if they roll a one on their saving throw.