from an M-500_ Mossberg shotgun!

I think it's a model 500C, but not sure!
Is there a special tool required?
It belongs to my nephew and he would like to stone it a little to smooth it out!

not a flame but if you don't know how to get it out maybe the knowledge to do any trigger work is lacking. anyhow its your gun so here goes. the front of the trigger group housing has two little lips that fit into the receiver so it can't be pulled straight out. push out the large pin on the side of the receiver above the trigger group. rock the trigger group up at the end closest to the stock and ease it out. depending how cruddy it is the shell stops may fall in. no big deal just take not which side they came from and put them back when you re install the group.

No offence taken!
It's just that I've never been around a Mossberg.
I've always used a Remington 870 pump shotgun!