Sometimes they just need to be racked a few hundred times to smooth it out also. Sit on the couch and watch tv while racking it back and forth (not that you perves) DO NOT DRY FIRE. Just use the forend release and rack. It will help it out.
Check Brownells, Sometimes they have 590A1 replacement trigger groups which are metal. There is an issue though using it on a Mav88. You will loose any safety due to the Mav has a crossbolt on the trigger housing and the 500/590 uses a tang safety on the top of the frame. From my experience the...
The only problem I see with this is it is listed with the grip as "non-removable". Well that kills the idea of stamping it and having a easy "build" of a SBS.