Awesome deal brother !!
Thats a steal. I agree, the gauge is off a little on mine as well. I try to fill to 3500 for my rifle fill, but its always a little lower. Maybe around the same 400-500. I prefer to just not go to the redline on my bottle anyway, since I dont know which one I trust more. Figure, I am still getting about 20 good shots per fill anyway, so not concerned. I may eventually get a bigger bottle, but like you said, it hardly gets even warmed up. Much quieter than expected as well. I treat my pump to the indoors of my office, so I dont have to worry about it getting condensation/rust or environmental issues in a damp garage.