Ditto on BBS, and I've also been fond of Shooter's Choice MC-17. I think many have strayed away from the really potent copper cleaners like Sweets 7.62 and the like, due to chemical damage of the bore an wear and tear on the cleaning brushes and jags. I imagine this Outers product may be similar insofar as it is in line with other strong copper solvents. Properly cleaned barrels that have left the barrel maker carefully lapped, and have been expertly cared for rarely foul - at least not enough to justify such a strong chemical cleaning and the associated risks and annnoyances. Also, folks aren't as fanatical about a clean bore - several barrel makers, including Ed Shilen have spoken out about the subject and none seem to be of the opinion that harsh chemicals and attemps to clean to 'spotless' have any favorable impact on accuracy. Some even warn that the use of certain harsh cleaners WILL damabe a bore and possibly void any warranty.