91-30 experts, need some information

I have a 91-30, hex receiver with a "D" on it.

Anyone know what that stands for.

Greetings,
The D is a finnish stamp meaning the chamber has been reamed and optimized for 7.62x53r 166gr spitzer bullet. You can still shoot 7.62x54r except for the heavier bullets. This is because the mosin headspaces on the rim and not the case mouth like say 30-06 or 308. You probably have a SA mark in a box on the receiver shank. And it doesn’t exist if you don’t post pictures