In order to have precise collision detection you need to use c_move instruction for the entities movement.
Imagine you have a player with a gun and a terrain (MDL). Your player needs to be moved with c_move (not ent_move or changing coordinates directly) and the terrain will have the my.polygon = on flag enabled.
Do not enable my.polygon = on, on moving entities, just in static objects, otherwise they will stuck each other.
