Theodore Christopher, Sorry about the attempt at humor in my first answer. The only time I saw anything like white sand on my new firearm was when a silica pack that they put in to keep humidity out broke. The little dry pouches they put in packaging may have broken some how. Check and see if you find a empty silica gel pack broke in your packaging.
Theodore, you should just do a regular clean/lube and if everything is kosher, no worries. If the action is still rough afterwards, I would contact both Buds and Mossberg for advice on resolution.
Buds does not open the boxes so how it came was the way Mossberg sent it out from Buds "Many new firearms are test fired at the factory. You may notice residual powder, rotation marks on revolver cylinders, residual cosmoline which sometimes appears to look like rust, etc. All firearms sold as "new" are in fact new in box as received from the manufacturer or distributor and include new manufacturers warranty....no exceptions."
Theodore Christopher, Never seen that before. What can I say. Firearm must of had a trip to the beach before you picked it up. Guess assembly debris. Clean her up and see what happens.