A few years ago, Remington sprayed a coat of hot cosmoline on their Police guns to protect them during shipping and storage.
At that time they recommended a treatment to remove the cosmoline and protect the gun in use.
This works very well for any pump gun.
Disassemble the gun per the owner's manual, including the magazine tube assembly.
Put the gun on a thick pad of newspaper and spray all the metal, inside and out, with a dripping wet coat of Rem-Oil or CLP Breakfree.
Allow to soak for 15 minutes to dissolve the factory lube and to soak into the rough finish.
After spraying the trigger group, stand it up so it will drain.
After 15 minutes, wipe off the excess, shake out the excess from the trigger group and wipe it off, then reassemble the gun and put it into service.
Of course, don't spray any wood with the lube.
The lube, especially CLP Breakfree soaks into the pores of the metal and builds up a protective layer of Teflon. This protects the gun from rust.
From time to time apply a thin coat to maintain the protection.
This method removes the factory preservative lube, cleans out any metal or wood shavings or particles, and protects the gun from corrosion.
Also, scrub the chamber with a chamber cleaning brush.