ksauers1, aside from a pocket knife, there are three things I always have in my pocket, and would feel naked without. One is a little 6 ft. Stanley tape measure that is about the size of two stacked silver dollars. Then there is a little folding pocket magnifier that helps with small details, proof marks, etc. And on my key ring I have one of those tapered bore and choke guages.
I've learned that there are lot of old doubles that have had their barrels trimmed either to remove muzzle damage, or to have more open chokes. Some guns can have an inch or more cut off, and the barrels still touch without any gap between. The first double I ever bought was a OO grade L.C. Smith. I owned it for about 10 years before I realized it had 27" barrels, exactly the way you described.
I know the tapered bore and choke gauge is not as accurate as a bore micrometer. But it is something I always have on me, and is a whole lot better than just guessing.
