As to dating cartridge specimens, I tried several years ago to make notes of when ammunition companies went by whatever name they were under at the time. (?) For example, ammunition made by E. Remington & Sons bore no headstamp. These are identified by the beveled rim and that they were of a caliber proprietary to guns of Remington manufacture, i.e. .44 Remington. When the Uninon Metallic Cartridge Co. and Winchester bought Remington, the H/S was "REM-UMC", the R-P, etc. Trying to determine the period of the company's existance was a help.
Mayb I'll ressurect my notes.