Only War: Tearing = two dice are rolled but only the highest is used.
So a damage of 1d10 + 6
would be 2 x d10 (remove the lowest value) and add 6.
There is a code for that: 2d10H+6
Of course that doesn't cover the possibility of the d10 exploding on a 10, and that would be difficult to incorporate since that requires another skill check in most WH40K systems AFAIK, so you'll have to watch out for that manually.