Next Question if they can build bombs they obviousely know how to built a gun. If that would kill someone, why don't they use it ? Why didn't Gatou who was like the Mafia and quite unfair use machine guns to kill Kakashi ? Or those Hunting Nins who sneak upon people ?
One villian would have used that if it was effective but then I think that there are people like Raikage and Tsunade and Asuma who can throw Kunai and Swords through trees making them even deadlier than bullets.
But if we say you had a gun and the enemies would have no chance to move or use a jutsu the answer would be "DEADLY" and we have proove because of Mangetsu.
Well it's not really relevant to this thread but i'd say the reason they don't have guns in this world is because learning a fireball jutsu is just easier. Gatou could've but Kishimoto has a very nonspecific fictional setting. Kunai are tradition and it might be similar to Feudal Japan where they were actively trying to stop guns from coming over or being made just to keep the honour of a sword.
There are also many ninja techniques which are identical to shooting bullets.
Kimimaro has digital scrapnel. Trollkage has water bullets which he literally shoots out of his hand as if it were a gun. There's the Asura path that can shoot missiles- Nagato even has a laser cannon arm. They're present- just in different ways.
Sasori! Because he's a puppet
True! He could take a shot to the head but what about in the heart bit?