I use gimp ;p
To use the bullets, its my secret ;p but Ill blab it since I want everyone to have good pictures! What you do is make a turret, turn the dmg off or turn on god mode and use the airboat tracers and adjust the spread depending on gun. Also, if u want a mg burst like mine, keep the time delay between shots on .10 if you want like an assult rifle, you will have to mess with it. To make it easier, also do host_timescale .1 and its 1/10 the speed in game so its easier to get better tracer effects