Don't know if its been posted but if you leave a shotgun in the cold I would check the parts are tight. Recently I was out to the trap range and it was about 35-40F outside, closer to the 35F it felt like. Anyway the first round of 25 went ok because the guns came directly out of the warm car and were put to work, however early in the second round two issues occurred (let the guns sit outside for 10 minutes while we warmed up).
1.) My gun has a plastic/polymer stock and it came loose, I'm assuming this is because the metal receiver shrinks at a different rate than the plastic/polymer and so the gap opened up between the receiver and stock. It didn't open up enough it was going to fall off but I still put it up after 6 shells.
2.) My friend's gun had the barrel come loose, again this is a situation of plastic/metal together. The mag-cap on an 870 is plastic and everything else is metal. He actually shot the entire round and claimed the funny noise was just crappy shells, didn't bother to check out the gun till the end and then he felt real dumb.