I have a long (30")? ribbed barrel for my 870.
Is it possible to cut some of it away, and re-thread the end to accept the rem-choke? I plan to keep it around 20" for H/D purposes.
I tried this same thing awhile back. Ill tell you about it and give you my 2 cents on the subject.
I have a Remington 3" 1100 with a 30" vent rib. I decided that a 26" would be better. I cut the barrel at the rib and chucked it up, dialed it in and cut it. I soon found out that the barrel after threading would only be around .006-.007 thousanths thick in diameter...which is WAY too thin. So thin in fact, that when I threaded it, it split right at the muzzle. So I had to cut it back. Same thing happened again. The threads, (32TPI) are fine anyway, and you could see the out line of them on the outside of the barrel. Since the vent rib is interrupted, you need to cut it at the ends to make it look right. After some unsuccessful attemps I ended up cutting the barrel to 18" and leaving it at that...with no choke in itl.
I eventually bought a 26" with a Remchoke in it and now have it on the gun.
There are a few choke systems that you can use, one of them is called "TruChoke". I'm not too fond of them as I have seen two of them blow the choke right out the end of the barrel. Some gunsmiths will buy a kit which requires handtapping the barrel, a method that can easlily get the threads started of center. The choke itself is only around .015 thick and had very fine threads that are easily stripped and crossthreaded.
The older 870 and 1100 barrels are just too thin to accept a Remchoke. After making several dozen chokes in various configurations and making several different patterns, it has been my expeireince that the RemChokes are the best thing going due to their somewhat longer length than the others. The longer chokes do pattern better, thats why you see extensions on the turkey chokes.
Do yourself a favor...buy one.