Well you got a half dozen responces from people that have never used the Foul Out , but know a better way . My son bought a used Ruger 77 MK II lefty in .300 Win. Mag . We are avid handloaders , so we went to work trying to work up loads that would give good accuracy and velocity . That rifle wouldn't group anything we tried , including several factory loads . So I got to lookig at that gun real hard . The bolt face had a very distinctive primer ring around the firing pin hole . I gave it a good scrubbing ( again ) and couldn't get a white patch out of it , still wouldn't shoot . A local smith had a Foul-Out so we let him have a go at that bore . I went back the following night to pick it up . He told me that he wanted to give it another treatment because the crap that came out of if was nasty . So the following night I went and got it . Evidently the previous owner was a handloader that shot alot of hot loads through it , without much maintainence !
We took it back to the range the following day , with some hand loads that my .300 likes . It was like a totaly different gun , it had become an moa shooter with a load that wasn't even made for it . I bought the Foul-Out II when it came out and have used it quite often on bores that were badly fouled . As far as I'm concerened it's the easiest , most thorough way to ensure that a bore is as clean as it can be . If you know that a rifle was clean when it got into your hands , regular cleaning with a good copper solvent is all that's needed . That was like 17 years ago , that rifle has accounted for at least two dozen Whitetails , a few bear and a big black Canadian Wolf .