I have a set of RCBS 308 Win dies that are marked 308 SB on the sizing die. Cases fit VERY tight in this die, so tight one is stuck now. Does the SB stand for anything special? Like small base or something like that?

Exactly like that. The RCBS "small base" dies are made for tight-chambered semi-automatics and other actions which have very little camming action to help them close on slightly tight cases.

However, the SB dies are a "fix" for a problem that only exists if the previous loading expanded the case head area significantly. If the load is expanding the case head, then it is too hot to begin with and should be reduced or abandoned.

I have never found the SB dies to be necessary for anything I've loaded. My recommendation is to sell or trade them for some standard dies. They should bring a premium from some guy who insists on stuffing his Garand so full of powder that the primers fall out after the second loading.

Only rifle I ever used them for was a Remington 742 autoloader in 308 that was a VERY tight chamber. If your rifle will take cases that are resized in standard dies you will be way ahead.

Thanks gentlemen. I'll sell/trade them.