Use you ring mandrel to size your ring base by wrapping the copper wire around it at the size you want. Wrap it around three times and leave the ends sticking out. (You need to hammer them flat.) Cut the wire.
Anneal the wire (make it soft) by heating it with your torch to dull red and quench in water. Hammer the ends flat on your anvil and sand of buff them so there are no sharp edges.
Put your base back on the ring mandrel and hammer the ends in place around it with a rubber or plastic mallet. Make sure the wire is wrapped tightly around the mandrel and there is no gap between the layers. You may need to hammer it for a while to get it tight. (If you have a gap, the silver may melt through the gap.)