Fit is way tighter than I've ever seen any 870 (like you need a mallet to remove it kinda tight).
Ridiculously hard to pump in both direction and sticks back (action opened) and forward (but is out of battery). I believe for different reasons, more on that when I check it a bit closer shortly, but I have my suspicions; barrel ring not to spec (too wide or misplaced), forend rubbing on the barrel (barrel is showing signs of rubbing). Chamber IS parked btw, but it looks pretty smooth so I'm not sure if this will be an issue. Due to the out of battery on an empty chamber I didn't even tried to run a snap cap in yet, so I have no clue.
Any barrel should fit any 870 except the MCS, the special field or the latest "extended mag tube" version. (Not arguing with you here, just adding to the exception). But to begin with NEA warns it might not work on a wingmaster, I guess they blame Remington not themselves.
870 are probably the gun I am the most familiar with for having re-built some old wingmaster/police, and being assigned to maintain those we are issued at work. I am no gunsmith, but give me a little more time i should be able to tell you exactly what is happening and why.
At this point I doubt I would buy one ever again, fit is aweful, finish is ok but nothing impressive and let's not talk about NEA's service...
Thank god I also dealt with SJ hardware this week, they are just awesome all around
