Savage 24S-E

I am new to the site, I inherited a Savage 24S-E with the 53U in a little circle at the back of the Barrel, I was cleaning the weapon and decided to remove the forearm, I
removed the bolt and felt something slip :confused: ? anyway I cannot get the forearm off and the bolt will not go back in, did something slide inside causing this problem? the weapon seems to work properly, of course I have not tried to fire it, was hoping someone could tell how to fix this problem. I have read several post about the number/letter circle so is this the serial number?