If you want a cheap, really cheap, way to measure the bores and chokes on .410 shotguns and the bores on rifles from the muzzle, go on ebay, search "small hole gauge" and you will find four gauge sets for about thirteen bucks and up. The largest of the four will usually be .400 to .500. They are what I'm using to measure the Model 42 barrels. They are just long enough to get past the choke, but they make it. You will need a micrometer or, preferably, a vernier caliper with dial or digital readout. I think they are about six bucks today.
