SG is smokin gun, the mad man of the Mohave.
C&R is a curio and relic license. It is a class 03 FFL. It allows you the ship C&R eligible guns directly between the buyer/seller.
Generally anything more than 50 years old is a C&R. BATF has a list of C&R guns, you can find it at their web site I believe.
I just ran across this on auction arms.
"California law will NOT allow shipment of C&R handguns direct to a C&R holder in the State of California, a 01 dealer must be used"
This may include cap and ball revolvers, I don't know.