Yes I am surprised, the airbrush is genuine Iwata, I have had them before. I thought maybe this could be a second or something. The quality is very good otherwise. I have inspected all components very carefully and am impressed with the quality of the needle spraying action and design.
I have for all purposes sort of solved this problem myself but the action still is not as smooth as my other brush. I would suggest for others just to return the brush and get another, I'm sure Iwata would honour this as it is a manufacturing defect.
I however have started fiddling with it now so don't feel right about sending it back and as I said it's working now ok, just not 100% maybe.
I imagine a chuck barrel and pin would be costly to buy on it's own, also these two components seem to be what gives the AB it's trigger feel. The other airbrush I have has defects inside this cylinder also just they are not causing any roughness or scoring.
Thing is I have heard reviews of other brushes having a better trigger action, if I were totally new to airbrushes and had nothing to directly compare maybe I would have accepted this and thought no more about it. I don't have an identical brush so I'm not sure if my brush is as good as they should be now or not.
I am tempted to use a jewelers file to remove all evidence of burrs on the cylinder and the pin then polish both surfaces and see if there is further improvement.
Anyway just letting people know it's worth checking out the trigger action on any prospective airbrush because some are flawless and when you have enjoyed flawless it's hard to go back to just ok.
Doug.