I have a 20 gauge Mossberg 500 from the 70s and I cant see any difference between the barrels it came with and the ones they offer now so I don't think the 12 gauge would be any different.

 

I have a 500a. Replaced the barrel a couple years ago. No issue at all.
Good luck

 

I just stuck a new barrel on an old receiver... Seems to fit just fine

 

Great! Thanks guys!

 

The barrel from a Maverick will also fit . This is a Maverick Receiver with a Moss 500 barrel.

 

If it is for slugs ??? Do not tighten barrel nut down, leave it a click lose, so barrel floats, so to say. If smooth bore.