It's also just manufacturing spooge. Mine had it everywhere and cleaned off with solvent.
Uh,no.It's not "spooge" it's rust.I bought a Mossberg a few years ago with the same issue.I noticed it in the store and picked out one with the least rust in the barrel.That crap wouldn't come out with a mop or bronze brush so I had to hone the barrel myself.Awesome shotguns but the folks at Mossberg needs to polish or spray some oil in the finished products.Anything to save a buck I guess?