Among other things, the barrel nut wrench is useful for tightening a loose barrel nut which isn't all that uncommon according to Belt_Fed who has told me he's received several 15-22 with the barrel nut loose. There are a couple guys who sell the wrench here in the 15-22 Classifieds *** 15-22 Specific CLASSIFIEDS ***. No crush washers or anything else involved other than the barrel and barrel nut. There are full video instructions in the Instruction Video Series here- Notable Thread Index