Stubblejumper, I wasn't real clear about the oil in the barrel. I should have said that it had a very light amount of gun oil, and it was more than likely in the grooves. What also could have happened here is the barrel just needed a few shots through it to get back its original point of impact. I used a midway 3" adaptor that is made of some type of cotton and put just a little oil on it so I get all of the cleaning solvent out of the barrel.
Curiousity makes me want to ask how much additional pressure would you expect if you did leave oil in the barrel.