Disclaimer - I do not guarantee the dates are accurate. I have tried my best to give the most accurate date information that I can, but as more and more information becomes available to be, date ranges can and do change (and hopefully become more accurate).
How the date ranges work:
After each date range, there will be a letter A, B, C or D (or combinations of the letters). Below is what each letter stand for:
A - The is the most reliable date range that I can get. It came directly from the manufacturer, their representative or their original archived records. Most likely accurate, but there is a remote possibility of minor errors.
B - This is the second most reliable date range. These dates are "commonly accepted" as accurate. Many come from archeology journals, peer reviewed professional journals. The reason that I have separated these date ranges from the above, is because I have not vetted the original sources personally. As I vet these ranges, some may change to an A date range.
C - C date ranges are comprised of approximate ranges gleaned from original, magazine advertisements and mentions in various period, magazine, books and newspaper articles. This is not the most accurate way to date a headstamps.
D - D date ranges are educated guesses on my behalf. I will give my reasoning for these date ranges. This will be the least documented and will probably be the least accurate.
Updating date ranges is an ongoing process. As I find more accurate information I will update the date ranges. I will also put the date that the information has been updated.