when I shot LBXR #6s I had sumtoy make me a choke. I sent him the barrel and he made me a .655. Grant it, it was a 21" barrel. years ago when I shot a full length barrel and any #6s "prior to lbxr" I shot a .660 With TSS I shoot a .665. A lot of 870 users like a .665 , but youll have to do the hand work yourself. You could very well use a tighter choke than that.