I wish to convert my 20g SW to slug gun for my son. The barrel nut looks different on 500s as compared to SW barrel nut. Does anyone know of a (18” or 20” preferably) rifle sighted barrel that will work.
Just a smooth bore barrel with rifle sights. 18” or 20” would be perfect. I have a hogue youth stock just need a barrel for conversion. If new guns were readily available is would buy what I needed. No need to chime in, I know I cant attach the stock until I have the 18” + barrel installed.
As far as NFA goes, scj3081 is correct. He can convert it to a "shotgun" if he prefers.
It's just unlawful to start with a shotgun and go backwards and put a grip on and then a shorter barrel, which is idiotic, but I don't think anyone ever said the government did anything that ever made sense.
With that said, as Ernst mentioned, you can use a smoothbore barrel with slugs no problem. And I'm even looking for a hogue stock in fde for one of my 500's. But I don't know if there is a such thing as an 18 inch 20 gauge 590 barrel. I don't recall ever seeing or hearing of one.
They do make 500C mossbergs in 20 gauge, but as you have noted, the magazine is different, unless you want to change it out to a 500c magazine tube along with the barrel may work.
Here's a link to the various barrels that Mossberg offer. Easy to view by model and gauge. That said, you could certainly shorten a barrel to the desired length within limits of the law. The big issue is the legal definition of an AOW, SBR or Pistol and which receiver can be used.