AN AUTOMATED APPROACH FOR IDENTIFYING CARTRIDGES.

        Cartridges are often recovered from historic archaeological sites. Standard guides to headstamp identification, notably Henry P. White and Burton D. Munhall's Cartridge Headstamp Guide (1977), can be used when headstamps are present. However, early cartridges frequently lack any identifying headstamps, forcing one to rely instead on measurements in an effort to identify the caliber.

        Data presented in the table below have been taken from Frank Barnes' Cartridges of the World (6^th Edition, 1989). We have used this spreadsheet to automate cartridge identification in the following fashion. After adding columns to the right side of the spreadsheet, we then write equations in our spreadsheet software to calculate deviations between measured values for base diameter, rim diameter, and case length with tabled values appearing in Barnes. Other measurements, such as shoulder diameter, can be added to the calculations if desired.  As an example, we recently recovered an unheadstamped cartridge near El Paso, TX, exhibiting the following measurements:

                                                                Base = .540         Rim = .458             Case Length = 2.32

        The Euclidean distance is calculated as the square root of the sum of the squared deviations between these three measurements and measurements appearing in the data table. In this instance, for example, the calculations would be:

                    Square Root of  ((Base_i -.54)² + (Rim_i - .458)² + (Case Length_i - 2.32)²) where i = the i^th observation or, in this case, cartridge in the list

        This equation (substituing of course your own measured valued) can then be copied to all of the cartridges in the list.  Identification is accomplished by selecting the match that has the smallest Euclidean distance or the smallest value. In this instance, the smallest value or best match is found with the .30-40 Krag-Jorgensen cartridge. A cross-check of shoulder diameter confirmed this identification.

        Note that cartridge condition directly affects measurements and, by extension, identifications. Don't use really battered cartridges unless there is no other choice. In some instances, we have only been able to measure base diameter (it is very stout) and case length. Even these two measurements can dramatically reduce the number of alternate possibilities that you have to deal with.  Also, try to determine:

        (1) whether the cartridge is a straight or bottlenecked case. 

        (2) whether the cartridge exhibits a rimmed, semi-rimmed, or rimless base. 

These two ancillary pieces of information, combined with a few measurements, can further narrow the field of possible identifications or, if you're very lucky, get a single match. Good luck and have fun! 

Oh, yes!. Tim Seaman, during his sodden, futile efforts to bag an elk during three days of driving rain, reminded me, while sipping Irish whiskey, that I had failed to mention that all these measurements are in inches. I would have thought this obvious since we Americans have refused to go metric. But Tim is the master of clarity and, in deference to his comments, I though I'd point this out. Thank you, Timmy, and better luck next time, you nimrod...