Normally an Actor that was hit by projectile or bullet gaines X and Y momentum, ignoring vertical angle between the actors and projectile. With ThrustZ flag a projectile will also thrust actor by Z axis.
Or must that be a console/compatibility option affecting all hitscans and projectiles? I'd like to play doom.wad with it. You can have some real fun with spidermastermind - set low gravity, try to jump on it, and he'll push you upwards with his chaingun

I also need this feature for realystic physics in my project. For now the only way to make actor gain z momentum is to use a projectile with radiusdamage.