I am going to be drilling up a formula for myself.  I just got it in.  It has been a while since I have thrown columbia.  My ball has a 1 inch pin a little shorter than I wanted but I am going to try to make do.  It has 2 3/4 top weight.  I want this ball to take off on the back end.  I want a good hooking ball for medium and also for it to get through heavy oil if needed. (which where I bowl there is hardly any heavy oil shots.  I throw about 17 mph medium revs, and I track about a quarter of a inch beside the thumb hole.  So please give me a strong backend drilling suggestion.  Thanks, Derek