Oh, you mean an EXPOSED bolt....
Open and closed normally applies to normal rest position of the bolt under the feedneck. Like autocockers are a "closed bolt" design and Nelson based pumps are a "closed bolt" design While most others have the bolt back and the feedneck open until you pull the trigger. THose being "open bolt" designs.
If your area is really sandy and you play that way then there's no doubt that sand or dirt getting in through the exposed rear of the upper bore will wear things out sooner rather than later.
But far be it for me to give you justification to buy a new marker and thus promote your introduction to rampant gun whoring....
