Proof Date Decoder
Early Glocks carry a three-letter proof date code stamped next to the serial number. It is a simple substitution cipher: the first letter is the month and the last two letters are the two digits of the year. Type a code below to decode it, or follow the steps to do it by hand.
Where to find the code
Look at the markings beside the serial number. After the serial number and the proof marks you will find three letters. Those three letters are the proof date code. In the example below the serial number is AA006, the proof date code is ATR, and AA is the prefix.
Proof code
Prefix
Do not confuse the proof date code with the prefix. The prefix is the first letters of the serial number. The proof date code is the separate three-letter group.
How to decode it
- Write down the three letters in the order they are stamped, for example C T F.
- The first letter is the month. Find it in the month table below. C is October.
- The second letter is the tens digit of the year. Find it in the year digit table below. T is 8.
- The third letter is the units digit of the year. F is 4.
- Put the two digits together to get the year, 84, and read it as 1984. Years 80 to 99 are 1980 to 1999.
- Put the month and year together: CTF is October 1984.
Worked examples
Month letters
| Letter | Month |
|---|---|
| E | January |
| L | February |
| N | March |
| B | April |
| S | May |
| Z | June |
| G | July |
| P | August |
| I | September |
| C | October |
| V | November |
| A | December |
Year digit letters
| Letter | Digit |
|---|---|
| O | 0 |
| W | 1 |
| K | 2 |
| R | 3 |
| F | 4 |
| M | 5 |
| H | 6 |
| Y | 7 |
| T | 8 |
| D | 9 |
Good to know
- The code gives the month the pistol was proof tested. It is not the date it was imported or sold, which came later.
- Barrel date codes use the same cipher, so this page decodes those too.
- Stamped letters are easy to misread. The letter O is the digit 0 in the year table, and letters such as I, S, B and Z can look like the digits 1, 5, 8 and 2. If a code will not decode, check each letter against the tables.
- The proof date code disappeared from US inventory when production moved from Austria to the United States. The proof process continues today for commercial production made in Austria.
To see every prefix and proof code combination documented in the registry, with its decoded date and serial number range, open Proof vs SN.