In the last episode of the first season a lot of special forces with machine guns attacked the Aogiri Tree. My question is, given the regenerative abilities Ghouls have, can they be killed with machine guns? If they can't be killed, what's the point of using them? And if they can be killed, what's the point of using Quinques if you can kill Ghouls with long range weapons?
Regular bullets can't pierce most Kagune, but there are special bullets used by CCG which are more effective. Q_Bullets, or Bullets coated with a thin layer of quinque steel, are enhanced bullets which do deal damage to Ghouls.
That being said, stronger ghouls are generally resistant to even those, as we see the top tier S and SS rated ghouls tank the bullets. Weaker ghouls are at risk of death as much as a bullet to a regular human is if they don't have good regenerative powers. You can see that best in chapter 60, which in the anime is 10-11 minutes into episode 11 of season 1, as the last few pages have Juuzo use Marudes bike to jump into a ghoul infested building, and he uses a machine gun to punch dozens of holes into a couple of ghouls heads, even showing them off in the manga.
No, I'm pretty sure bullets can't hurt them.
Like, when Kaneki was considering that he was a ghoul, he tested it by stabbing himself in the stomach with a knife. Needless to say, it didn't work. So, ghouls cant be hurt by knives. Bullets are basically just tiny, blunt, round knives traveling at 'superfast' levels of speed (or, whatever, work with me here).
Quinques are the only weapons used against ghouls - considering that firearms were introduced to Japan in the 13th century from China, and quinques were invented like, waaaay after that, it stands to reason that guns don't work, or else no one would have bothered inventing the quinque.
"But, Kat, machine guns are different to normal guns!" I hear you, dude. But the logic moves up a step from, 'if a knife won't kill it, a tiny, blunt, round knife travelling at 'superfast' levels of speed won't kill it either' over to, 'if a tiny, blunt, round knife travelling at 'superfast' levels of speed won't kill it, then an absolute load of tiny blunt round knives shot in a rapid-fire hailstorm of death probably won't kill it either'. What it will do, though, is slow it down!
It's like someone firing a paintball gun at you, except the paintball gun is a machine gun. It's not deadly, but it's going to give you some bruises, distract you, slow you down and annoy you!
Bullets can't kill ghouls or badly injure them, but they can give them the ghoul equivalent of a paintball bruise, distract them, and slow them down.