My RBL had a loose fore end. I even sent it back. When it came home, the problem was solved for 200 rounds or so, then it got loose again. Costing me the freight.
Well, tonight I figured it out. The freaking screw on the fore end was somewhat LOOSE. What a dummy I am. Tightened it and now it's bank vault tight. I could have saved the shipping costs.
I hope none of you are as dumb as I am. The screw was loose and I should have figured it out immediately, but the screw looked tight.
I'm only posting this shameful post because I hope it will serve any others having this problem or those similar. There are a lot of screws on most shotguns and the first test is to see if they're tight. I assumed they were, but they're worked loose, and a drop of Lock Tite would have solved the problem forever on this good gun. Get a great gunsmith screwdriver set is my advice.
I am not a very good do-it-yourself guy.