The easiest way I can think of identifying unknown cartridges is to first organize and document their dimensions: neck, bullet, shoulder, base, and rim diameters, rim thickness, case length, and headstamps.
Next take these dimensions and try to find a match in Cartridges of the World, by Fred Barnes. There are others, of course, but this is the most easily available at your local book stores.
Digital photos compared to known cartridges and with the dimensions should be enough for a positive ID/
HTH
John