Chamber polishing on a MM

[Bourget117]

I've read on this forum as well as many others that the 870 express ,regular and marine magnum, benefit from a chamber polishing. After inspecting my new marine magnum a little more, I noticed that the barrel had a few rough and sharp spots on the extended tab where the barrel meets the ejector spring. I think someone on here told me that it was fairly normal and may smooth out after more firing. But when I stuck my finger into the chamber I noticed that it is mirror smooth and shiny. Is this the finish that every talks about needing to be polished more? Because it already seems as smooth as it could get right from the factory.

[TexasArmor84]

Mine is the same way mirror shine on the marine magnum. I had an issue when had my parkerized 870p it had parkerization inside the barrel and I had to polish it probably goes for the express finish as well


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[Bourget117]

So I guess us marine magnum owners are pretty lucky that the chamber is about as perfect as you can get a barrel straight from the factory. That's definitely a big bonus.

[Synchronizor]

Polishing the chamber is meant to help smooth out the finish there, to aid in extraction. This will happen naturally as the gun is used, but since so many of the shotshells on the market use steel cups these days rather than better-functioning brass (even most brass-colored cups are actually steel), smoothing the chamber's finish can help ease extraction with cheap ammo in a new gun. The Marine Magnum nickel plating is probably naturally smoother than the Parkerizing or bluing most other 870s are finished with - which are somewhat rough & porous on the small scale.

Oxide- & phosphate-finished chambers also come from the factory with a protective layer of grease, which can make extraction difficult if it's not cleaned out prior to shooting - as per the instructions in the manual. Nickel plating doesn't require a grease or oil after-finish to protect against corrosion, so presumably this step is skipped when Marine Magnums are manufactured.

Note that a rough finish is a different thing from dings, gouges, or poor machining in the actual metal itself. These are actual defects, and need more than simple polishing to correct.

[rottdogsparky]

Pictures anyone?

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