I have had 300 below do a few pb barrels and some knives for me. I have not had any airgun barrels done. My results were mixed, but totally amazing. First, there isn't a negative, except time and some money. Second, miracles do happen. Most of the barrels and knives didn't show much difference so I wouldn't try to sell anybody on it unless you have already tried everything else. Then why not? However I had one bull barrel from Foxridge Outfitters in .22mag that shot 9" groups at 100y. The crown and the chamber were perfectly done, I couldn't understand how a barrel could shoot so badly. I said, what the hell, and shipped it to 300 below. When I got it back it shot 3/4" groups with the same ammo it had been doing 9" groups before and these included Winchester and CCI hollow points and solids. Everything shot great after, it didn't even have a preference. Will this happen for you? Probably not, most likely not, I still don't know how it worked so well for me, this one time, but it did. So, if you have tried everything else, checked the chamber and the crown and the bore and you don't want to just throw it out, try it. You don't need to understand success to appreciate it.