There is more to the garret formula than meets the eye. He is using a super hard, heat treated mono-metal solid with a huge metplat and very high sectional density. This allows him to slow them down to 45-70 velocities. If you really want to understand the relationship of metplat to wound channel, go to http://www.gsgroup.co.za/articlepvdw.html It is a bit technical, but very interesting.