The bullets will be as fast as real bullets. So a 7.6 mm bullet will fly at 833 m/s.
This may not be enough, if you cover 1 meter in 1 frame, you might miss a headshot.
How so?
At 800 m/s and 60 fps the bullet would move 13 meter per frame.
The thing is, when actors have collision enabled, the engine will use sweeps during their movement to determine if they collide with something. Making a raytrace is (should be) the same.
relaunch it again, in the same direction, slowed down/with less energy.
That should work, too.
However in this case I would need to make sure, that the bullet can spawn behind the target without colliding. Also when the target is moving away from the bullet and moves first, he might move into it and get hit again.