Buy a tap and drill at the local hardware store. 1/4-20 works for most .308 heads, 10-24 for the .223 heads. Drill and tap the head of the shell. Use a socket that clears the case head but catches the die (about 5/8 for a .308. about 1/2 for a .223) and run a screw with a nut and washer through the square drive and into the case. Screw the nut down against the socket and the case will come out.
I have all the things needed, so this is simpler than buying a stuck case remover. They work the exact same way.