OK, I got out my Vernier caliper and my "small hole gauge", the cheap way to measure .410 chokes. My 30" .410 is a real horse, seven pounds, two ounces. Right muzzle .400, left muzzle .390. Don't know the exact bore diameter, but if it's .410 or anywhere near that, we have serious choke. My small hole gauge is pretty short so it probably won't go deep enough to get a reading on the bore, but I'll try next time I get a chance.