The short answer is trial and error, but the true answer is that I had a specific action I was after so I just kept moving the center of balance/gravity lower. To get it lower, .... well view the below video (short) then I will continue.
http://s1151.photobucket.com/albums/o62 ... 050931.mp4Larry Dahlberg, in his DVD, mentioned that when he makes shells he addes microballons to get it to stick to the sides better. I tried to go straight, but the shell was hard to get consistent. When I added microballons, the shell formed much better, with a lot less overall material. With the thin but though shell, I could then add weight. At first I would let the Alumilite White/ballons mixture set up. This was nice in that I could use alumidust and not have to paint (# 9 lead shot did not show), but again, the center of balance was raised by the thickness of the shell. Now I add the shot before the Alumilite White sets up so that it drops the center of balance a little more.
Please don't get me wrong, I am going to use the lure that I showed in the video where I got the COB higher, but it will have a different action. The original S-Waver is a wake to shallow running lure. Some time ago, while taking a friend of a friend out fishing, I was dealing with the guy getting snagged or tangled all the time. The S-Waver would slowley sink to the bottom. When I got the other guy fixed up and started to retrieve, I would get hammered. It tought me that I needed the same type of lure that would run deeper.
With a higher COB the lure has more lateral rolling, spilling water quicker, changing the "angle of attack". This is what keeps the original in the top couple of feet of the water column. By changing the COB and by not adding the lead shot to the back section, I was able to get the action I want.
I did try to just use straight Alumilite White for the shell and then use the microballons for the rest, and the COB was just not low enough. I also tried just using the Alumilite White with microballons, placing the shot as I do now, and again, it was just not as low as I wanted. Still, both options gave great lures, they just ran more shallow then I wanted.
I hope this helps some.