This is the 2nd version of TP ground impact system.Now impact direction(particles for FumeFX) is affected by collision object's surface normal and bullet's reflect angle.

As you can see in this movie,when impact direction is affected by only surface normal or bullet's reflect angle, the result is unnatural. Blending both surface normal and bullet's reflect angle make it much better.In this case, main plane object for Fume particles should be parallel to the collision object's surface to avoid strange intersection between emission area and ground.

It's tricky to calculate bullet's reflect angle. The equation to get reflect angle is "2*(V * N)*N - V" V means bullet's incoming angle(direction).In this case, bullet's incoming angle should be normalized(make it between 0 to 1). N means collision object's surface normal. In this movie, I multiply -1 to invert result. When I tried to make this effect,k240(vimeo.com/user4477453) told me this equation. He's so smart:-)

At the last part of this movie, smoke is so bad because of low resolution. I have to research better smoke setting. But it would be nice if you can find this system is so easy and flexible to make such kind of effects.