if u r still getting nice groups, why worry about it? if it was the brass jag, the metal shavings would appear yellow. If not, then it's not the jag, now is it? I'd say some residual shavings from the rifling process were left in your barrel, when it got shipped. There's no need to clean a 22 rimfire bore. Just the action, chamber, boltface. Cleaning it from the muzzle is likely to do more harm than good, with the cleaning rod flexing enough to contact the rifling. Soft aluminum rods can have abrasive primer residues get imbedded in the sides of the rod, then you are rubbing that abrasive up and down a soft metal surface ( your .22 rifling) which is eventually going to be a bad deal.