I have to admit the 373kJ value I came up with would probably be a little off. For a start I didnt add any of those 6 teeth, and secondly, as Hardox is not an option with the Kinetic Energy Calculator I just used Steel. When calculating the ring I got the same as Paul - around 38kgs. Again, as I was using Steel it isnt that accurate, but Leos value of 75kg seems a long way out. I get Steel at 7750kg/m3 and Hardox 400 at 7680kg/m3, so where did I go wrong?