RE: Installing choke tubes in fixed choke barrel.
I too have had Briley Thinwall tubes installed on a couple of fixed choked target O/U's and while they perfrom very good, I would think getting a new Rem 870 barrel with Rem chokes would save you in the end. With the Rem choke type you have and endless array of aftermarket tubes while the Thinwallscan only be hadfrom Briley. Oj course each barrel is different and if your smith can cut a stanard threads in your barrel then that would probably be the most cost effective and easiest.