Danny the barrel should have markings on it underside near the chamber something like 18.4 ,,, which would be your bore dimension you have to convert that to a decimal, your choke is what it is, to be sure of the constriction you have to get it measered, the one I had was a 40 but you dont know for sure what your is until you measure it, they are not all the same. Tony
Scott. I would asert that your bore mike is "off". Few if any barrelsmiths will alter a italian bore by such few numbers. Seitz used to like .740 and about .032 const. I have no recent experience with Wilkinson, but I'm guessing he is likely at soimilar numbers. Those bore and choke IDs are kinda common and have been fo ryears. I suggest that you get another opinion. And it is possible that yor TM1 came from thefactory like that, with those dimensions. It could be too, that you have plastic build-up in your choke region. Cleand the bbl, re-calibrate your mic and give us a report.