Yes, I made a typo How would you measure 6" into the barrel?Bill M. said:You need to measure both the ID of the barrel about 6" from the muzzle and the Id at the muzzle. I would check the .615 number with some other sources. I think that is a bit low for most 20 gauge guns. Your .004" is a typo. full chokes are generaly about .040 in constriction.