M47 1943 AA serial prefix (and then there is this... pic)

[Riflechair]

What the heck is this?

I'm dang fangled
"A" "B"

I'm not sure if these letters are together "AB"
OR
If they each have a seperate meaning.

This rifle is not FTR'd.

 

[Claven2]

Likely just inspection stamps IMHO.