again someone correct me if im wrong but, You can put any barrel from any model 870 on a different finished reciever.quote]
actually in the late 70s the 20ga 870 was on a 12ga frame. this was only done for a very few years. the barrel is diffrent, it kind of necks down and isn't interchangable with any others. i believe all the rest are though. the only reason i know this is i bought a 870 with my bailing hay money when i was 11 and it was this necked down model i was talking about. it had a slug barrel on it and 10 yr or so down the line i decided to buy a 28 inch ventelated rib barrel only to find out the chances of finding that barrel are about as good as leaving the 1500 tomorow with a 400 dollar ar-15. i still look at every show and online and never found one.