I answered this and lost it on transfer so will shorten this one and try to get my point across in fewer words. When some one uses JB on one of my rifles I void the warrantee! For two reasons. ! it dimensionally alters the barrel dimensions and not evenly and the second reason is the barrel maker laps the barrel with a grit of lapping compound that is most effective in preventing metal fouling. Then a customer polishes that finish away with JB.
I wouldn't be as apposed to it if it were applied on a lead lap and very sparingly. It is very obvious when you look at a barrel with a bore scopes all the sharp edges are worn off the rifling. if it has JB used on it on a regular basis. As you know ,it is an abrasive of about 1000 grit. As for using it on factory barrels I will say that while it is difficult to hurt a production barrel but the thing that hurts a match barrel will do the same to a factory barrel