I can answer that easily, it's a "q". There is no "g" suffix byf41 Lugers. They start at the "n" block, go to the end of "z", start over at no letter and go to the "b" block or so. You can find 42 1940 g blocks, and byf42 g blocks though.
https://luger.gunboards.com/showthread.php?3695-1940-1941-DATES-MILITARY-CODES-42-and-byf-DATA