If alterations to a silencer would increase the overall length or change the diameter or caliber of a silencer, this is the making of a new silencer, as opposed to a repair. The new silencer must be registered and transferred in accordance with the NFA and the GCA. Alterations to a registered silencer that result in a minimal reduction in the overall length for purposes of rethreading are permissible as repairs. However, the reduction in length may not result in the removal, obliteration, or alteration of the existing serial number, as this would violate 18 U.S.C. § 922(k). If such a repair is necessary, the damaged silencer should be destroyed or returned to the registrant. If it is destroyed, destruction should be reported to the NFA Branch. Any replacement silencer must be registered and transferred in accordance with the NFA and the GCA. See also “May a Federal Firearms Licensee repair a silencer by replacing worn or damaged components?” and “May the outer tube of a registered silencer be repaired due to damage? If so, may the repair be done by someone other than the original manufacturer?” for further information on repairs.