Mosin Nagant M38 marking

Hello,
I have this M38 Mosin Nagant ,and asking to see if anyone knows anything about the letters and numbers (GY 00) stamped between the serial number and manufacture date on the barrel shank. All the metal parts have matching numbers, but the stock is the M44 version with a different number. Thanks

P.S.
Happy Fathers Day!
Attachment 118145

'G' 'Yoo' are the transliterations of the Cyrillic G and Yu characters below them. And Happy Fathers Day to yoo too!

Well, thank you for explaining those extra letters and meaning. I never thought to look for cyrillic matches. These are the first ones I'd noticed on any of the Mosins I've owned.
Rick