Mr. ManBearPig:
If I may add my thoughts to this Discussion.
First off, I think that the 870 is one of the most versatile platforms out there and can be adapted to almost any task from shooting clays, to deer hunting with slugs, to defensive shooting with buckshot. There are a multitude of accessories available, and if any new and funky accessories are made, it’s a pretty sure bet that you will be able to find it for an 870.
That being said, like anything product line being built and sold, there are certain models that are of better. Over the last 5 years of so I have built several guns both for trap and defensive shooting applications. All have been for my personal use. Until recently, all of the guns I have assembled or built have used 1960's, 1970's, and early 80's vintage Wingmasters. If it was not a wingmaster, I was not interested.
My favorite are the 1960's vintage, and for several reasons. First these guns are machined from solid steel, and have a higher degree of metal fit and generally finish when compared to the express models and even recent manufactured Wingmasters. As a result, they tend to be one of the slickest 870 actions out there. Second, these guns are fairly easy to find in good to excellent shape, and can be usually be purchased between $200-$250.
There is a trade off with these older guns, being that you will not find one that can take 3" shells, with the flexi-tab system, or ready to shoot steel shot, but all of these short comings can be easily remedy by a smith that knows his way around an 870. (Insert plug here for Repete & Arwen Ace)
Recently, a good friend of mine (none other than CGN’s Easy) brought to my attention that the 870 Police magnum with its all steel construction, and superior metal fit, and durable parkerized finish also bears consideration. I was unconvinced until I had a close look at a 20" police barrel. The workmanship on this barrel was superior to ALL recent manufactured 870 barrels and on par with older manufacture barrel, yet having thicker barrel wall which provide a strong basis for some pretty interesting projects. I was so impressed that I just purchased a 870 Police magnum action, and look forward to putting it through its paces. (Insert shameless plug for future shotgun post submitted by myself

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This recent revelation, has led me to start looking at other 870 type shotguns as well. I am still not impressed with the 870 Express versions, however I am starting to think seriously about the Norinco HP9-1 14" barreled Shotgun. Allow me to explain.
If one Steps back from just looking at Norinco Shotguns, and has a hard look at the entire product line, the one gem that truly stands out is their 1911 line of pistols. Norinco 1911 frames and slides are highly sought after as the base platform for many full custom builds. The reason being is that these part are made of some of the hardest medal/steel in the industry (This comment comes from Gunar at Armco) and as such are desirable for the longevity expected from such metal.
It is my true hope that the H9-1 is the "1911" of the shotgun line. However only way to tell is to see one "up close and personal" and put it through its paces. To that end, BadBoyBeeson is selling off several HP9-1 receivers inexpensively, and I am buying one to fool around with, and to have a good look at what these Chinese shotguns are all about. Heck for $160 spent I thought is was tough to go wrong, a great way to gain some “hands on experience”, and perhaps an opportunity to find a “gem in the rough” so to speak.
Now, ManBearPig, from your post it sounds like you have already purchased your gun. If I were you, I would send Repete a PM and see how much it would cost for him to slick it up for you. While your at it, I would be inclined to have him replace the Norc/Express trigger group with a Wingmaster trigger group, and make sure the hammer engages the firing pin at the correct angle. Next I would have him replace all the remaining coil springs on that gun with a Wolf spring’s, a good anti bind follower, and then I “would go to town” and shoot the living begeezzes out of that gun, making notes and observations along the way.
If you are fortunate enough to have an HP9-1 with a 14" barrel, do not let it go. I had several discussions with our own CGN Brobee, (one of the original builders of the 870 CQB system) about those barrels. It was his opinion that the Norinco 14" barrel was one of the best barrels on the market at the time as the did indeed have moderate amount of choke (some where between Cyinder bore and Improved Cylinder) and that they had great forcing cones, both of which lead to good patterns. All of this was further born out in the empirical work he did with regards to patterning and gelatine penetration testing.
Sorry for the rambling, but these are my thought, and I would be glad to hear any and all observations the rest of you might have.
Regards and all the best
AbH