I went to Zales and found that my finger is about size 10, which comes out to about 20 mm across. I'm going to do more measurements to be more precise on how much I can bang away before its too late. I don't mind it being a skinny ring anyway.
I did drill the center out, which was rather difficult since I don't have a vice. I had to hold the thing or put it on the floor. I actually made sure to bite down in case I went into a finger. It will be a breeze to dremel out the rest of the ring when the time comes.
The Ring as of 6/21/09
I can't understand for the life of me why the other guy took a year to form his ring. I've been going at this for five days and have accomplished a considerable amount. I think it is because he is holding his quarter while he taps. When he holds the ring and taps, the quarter naturally moves when struck lessening the blow. My method is such that I place the ring on my computer desk running parallel with the wire frame. The desk has a beveled edge like a spoon, so I'm essentially bashing two sides with every hit. The rounded corners allow for a nice centered strike on the bottom. Bear in mind, I usually put a sock doubled over in between as the banging can be very loud.