hey Shoening..you may need to show an example capx...
collision detection is based on the Collision mesh ..if its too small then yeah the bullet may pass through undetected..
your ideas are good for trying to prevent this ...
but it comes down to specific solids and the meshes ..would need to see a demo or capx to really break it down and see what is happening..
you could try using delta time scale and slow it right down to see if there is another problem ..
like on start of layout set time scale to 0.2 or something..this might help you see whats going on...it may not either but it could point to your bullets being too fast..to activate the collision events on certain meshes