They are not cheap, as postoak and Larry mentioned. I was fortunate to have won three $200 gift certificates from Briley. They threaded the MX-8, sent me nine S1 tubes, a choke tube "rotary" cleaning brush and a speed wrench for the certificates. I shoot Comp-N-Chokes in the MX-8 mostly, and want to get the BSS threaded to use the set of Briley tubes in.

There is plenty metal at the muzzles of mine. They measure nearly .060" left, and around .052 right.

May God bless America and those who defend her.