Many thanks to everyone for the informative responses on this subject. I've read all of them with much interest.
Chuck, can you tell me where to find the articles by Sherman Bell? It seems to me that a 15% rise in chamber pressure caused by shooting a long cartridge in a short chamber could be significant in terms of safety. In any event, I plan on using shorter hulls.
After reading the responses by Researcher, I went back and re-measured the chambers on my NID. I believe my method is okay: I made a three-inch-long wooden plug that just barely slides into the chamber, pushed it ahead until it met resistance, then drew a fine pencil line flush with the breech end of the barrels. This again measured 2-11/16". It does not appear to me that the chambers have been lengthened (no milling or polishing evident), all of which makes me wonder exactly how the chamber length was measured back in 1927. I've been assuming it's measured from the face of breech to the beginning of the forcing cone. Is that correct? Because I will be using short,low pressure loads, it might not be all that important, but I'd like to know just out of curiosity.
Any suggestions for further reading on the NID will be much appreciated. This seems to be a fine old shotgun and one I look forward to shooting and taking to the grouse woods.
