Storm - Taylor tested Hoppe's #9 Plus a couple years ago over a 5 day period. The barrel was loaded with a very wet patch (normal for us) of Hoppe's #9 Plus, then put outside overnight, brought back inside, put out again the next evening (or day, etc,) for the 5 days, then the plug was pulled powder removed and carefully expamined for powder contamination and for rust. There was not of either.
The only difference I found, was that Hoppe's Plus, like LHV, required 10gr. more powder to get the accuracy back over what shot well with a water based lube. That was in both the .40 and .45 rifles. It's slippery enough in my barrels, to give a slick barrel 'event', where more powder is needed to get a good even pressure shot to shot, which results in good accuracy - that's my theory and i'm sticking with it. If a barrel is a bit rough or has some pits, maybe it won't have that effect?