Hoppes may be the worst case trial in cleaning ability that I know of in modern firearms if he was using the old hoppes # 9. The newer Hoppes elite is good stuff, the #9 is pretty much a kerosene that does decent only at removing powder fouling... If you want to see that barrel come clean then use wipe out, this is the best cleaning solution for guns that i have ever used, and I have spent hundreds of dollars testing !! I'm sure the zmax is not even touching the copper which is the main issue in a 22-250, and yes even extreme match grade barrel makers like Lilja etc a 22-250 will be shot out after 6000 rounds for all general target purposes, but then again you have to remember that most people are happy with boxstore accuracy of low priced firearms around 3" group... not to say there are not exceptions to the rules in prices=performance when it comes to firearms, but it's few, and far between... I consider accuracy starting at .25" extreme spread at 100 yards, and if I'm sgooting for accuracy I want much less than that !!
Now for this zmaxi stuff I may just have to give it a GO, I'm 99% of the time against any additives.