Any new 870 should have the stock and fore end removed. Remove the bolt from the stock. Spray it out with carb cleaner. When dry spray some Eezox inside the receiver and inside the fore end tube. Wipe it down while wet with Eezox and reassemble.
If it won't run 1000 rounds without issue after that get rid of it. I am with Battue on this one. I have dropped an 870 overboard into loon [bleep] and all it took to keep going was to jack the shells out of it and then work the action in water a few times.
I walked into an 870 marine magnum that had so much plastic in the barrel that it took a whole can of carb cleaner spray and a brush chucked up in a drill, yet it still worked just fine.
DId all that just recently on my 10 year old 870 still rough as a cob.
