My new 870 Express is getting a few light surface rust spots I don't want. Any non-greasy coating I can apply inside and out to prevent this? It's a working HD and truck gun. Thanks.

Rub the rust off with 0000 steel wool, and Break-free. Don't know what environment you are in, but might consider waxing it, if gun oil isn't doing the job.

The best way to prevent rust is to apply a light film of rust inhibiting grease (Hoppes, Outers, RIG or whatever) to the exposed metal. I have used gun grease for many years and have never had a rust problem on any firearm so treated. All the best...
Gil

This seems to be a common problem for new 870s. best solution is to keep is well coated (with oil or grease) for the first year. After that it seems to be a lot less prone to corroding.

Thanks for the replies. I took it all apart to the subassemblies (didn't dismantle the trigger group) and cleaned it well. Then I did the Johnson's paste wax treatment inside and out, let it dry very well overnight and buffed. Put it back together and gave it a final buff with an old washcloth. We'll see how it does. Where my hand grasps the receiver while carrying is the most rust-prone spot. Might drip some water on an open area once of it to see if it sheds water. Hope so. If this works, may make a wax rubdown a routine treatment.

Over on Shotgun World, they have been dicussing (and cussing) this problem on the Remington 870 Express guns for some time. What appears to have happened on some of the runs of this gun was they did not get a good final bath after that grey finish. No big deal, except to some. The answer is so simple that some people can't seem for it to soak in. Mix Bicarb soda and water. Wipe off the oil with acetone. Wipe the entire surface with the soda/water mix. This will kill any of the action. Dry the gun well with a hair dryer and oil with any good oil like Breakfree. We have done this to all of Dixie Slug's 870 test guns.Maintain the finish like any blued finish......James