There is some confusion between the term chamber length, and the length shell a gun is chambered for. SAAMI specifications call for a 12 ga. chamber to be 0.7980 inches +/-.005 inches at the small end of the chamber. The chamber length of a 2 3/4-12 ga. gun is specified as 2.750 +/- .05 inches. So chamber length can vary by 0.100 inches. If you take the time to actually measure chamber length, you will find that they often use up most of the allowable tolerance. Of course, you may not be able to tell whether a previous owner has gone in with a chamber reamer to remove a defect. I still have never seen a 12 ga. Smith with chambers shorter than 2 3/4 inches. Some have pointed out that many Smith guns predate SAAMI specifications. We still have to use some standard, and even Smiths from the 19th century appear to conform to the SAAMI requirements.