LETS CAUCH THE SUBJECT FROM THE BEGINING .1 GUN HAS A BARRELL , 1 BARRELL HAS A CHAMBER AFTER THE CHAMBER IS THE FORCE CONE ,AFTER THAT IS WHAT I WANT TO KNOW SO HOW U CALL THAT? IN MA BROWNING GOLD THAT HAS 18,8 MM ,AND THAT TOLD ME THE MANUFACTURER SO IN M2 NOWONE SAYS THE EXACT DIAMETER OF THAT?4 EXAMPLE THE MANUFACTURE ? AFTER THAT WE GOT THE CHOKES DIAMETER U TALKING ALL OF U ABOUT ,I TOLD U AT FIRST MUST BE MA ENGLISH THE PROBLEM.