I've always wondered if the reason that the Challenger Plainsman CO2 rifles are so rare is that they had the tendency to rust. Any CO2 gun will sweat, especially a bulk fill gun. The metal finish on the Challenger Plainsman was really not up to the task. If the gun was not cleaned and oiled before putting away, it would rust. I suspect that most CP CO2 guns ended up in the scrap bin, due to rust.