adbramsay,
Read That Fine Manual which came along with your 870, and get comfortable field stripping it and reassembling it. It's a little bit of a learning curve but shouldn't be too bad, if you have a family member or friend who's already well versed in the process, having them on hand the first time out might help.
First thing to do is make sure all the excess packing preservative is removed from the gun, if it was brand new. The stuff is like cosmoline in some ways but I've found WD-40 will help get it off. Be especially sure you clean out the chamber and bore to get rid of this stuff. It'll look brown on a clean cloth, but it isn't rust. What it WILL do is act like glue when it gets hot, and it can help make fired shells stick in the chamber.
As far as broken parts on an 870, that happens very seldom. Depends on how much ol' Murphy likes you, I guess
. A lot of 870 armorers use just a cigar box for a parts box, because they seldom need much in the way of parts. The only really troublesome thing on an 870 to damage is the magazine tube. Replacing it is a factory repair center job, so you want to be really good to your magazine tube. Putting on magazine extensions without barrel clamps
is not being good to your magazine tube, those threads on the end are pressed into relatively thin sheet metal and a long extension acts as a lever to exert force on those threads if it is not braced by a barrel clamp. Dents can happen to magazine tubes sometimes too, but many gunsmiths have a dent remover for 870 magazines (
http://www.brownells.com/.aspx/pid=25276/ttver=2/Product/MAGAZINE_TUBE_DENT_RAISER ). And I haven't seen an 870 magazine damaged between receiver and forearm so far that the gun wasn't being used as a pugil stick or something.
Bought a 5-shot 870 Express and you want to put a magazine extension on it in spite of the magazine tube dimples? I'd forget about it, but that's just me. I've seen Express magazine tubes beaten out of round by people trying to iron out the dents with a socket or the like. Drilling them out is usually the cleanest way to get rid of them, but then you remove the ability to go back to a 4-shot magazine without kludging up some way to keep the magazine cap tight. All in all, just not worth it IMHO, but YMMV.
IMHO the easiest way to be prepared for mechanical problems with an 870 is to have on hand a complete spare trigger plate assembly, a complete spare bolt assembly of the correct type for your gun, and a pair of shell latches and the proper staking tool for them. Ejectors on 12 gauge 870s (the spring type) occasionally break but not often, as long as the owner is careful in cleaning the receiver. Replacing an ejector means drilling out a pair of small rivets, removing the rivet heads from the side of the receiver, replacing the spring and re-riveting it in place. Not something the usual owner is going to want to undertake, and the repair will look pretty Frankenstein-like if the receiver isn't refinished properly. With a single 870, I doubt I'd worry about any of that, unless I was going off to the ends of the earth and the 870 was the only gun along. Even so, everything described in the above paragraph would weigh less than a box of 25 shotgun shells, and not really take up much more space than a box of shells either.
http://www.remingtoncountrystore.co...ber=3&catalogid=1&categoryid=3566&topcat=1038 will give you factory pricing but sometimes parts turn up cheaper, if you look around.
One other thing I'd keep on hand is a couple of spare magazine springs of the appropriate length. I use replacement springs from Wolff -
http://www.gunsprings.com/Rifles & ...878, 11-48, SPT-48, SPT-58/cID2/mID108/dID216 . Store them in appropriate lengths of PVC pipe with pressed-on caps to keep them in good shape until/if needed.
Probably more than you wanted to know, but...
hth,
lpl