This guide explains the purpose and application of witness marks on firearms. Witness marks, typically made with oil-based paint markers, are used to quickly verify if critical fasteners or sight adjustments have loosened or shifted. Applying a line across a fastener and its mating surface, or across an adjustable sight knob and its body, allows for an immediate visual check. If the lines are misaligned, it indicates a potential issue requiring re-tightening or re-zeroing. The process includes removing old marks with alcohol before re-applying new ones after adjustments.
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