I think most everyone here is missing the obvious part of the problem.
The guns and whatever propellant they use to fire the bullet are not the problem. Its the user plain and simple.
If I want you dead disabling my gun powder wont stop me.
I can still shoot you but I just have to change my propellant to something else like a high pressure gas as in shoot you in the head with a simple ball bearing shot from a common paint ball gun that has been turned way up.
Now what are you going to do? Take away all forms of compressible gas?
Even then if I cant shoot you I can get a sharp pointy anything and stab you in the eye or ear with it. It may not kill you but if I do it right I can scramble enough of your brain to basically render you a vegetable or at least too simple to ever cause me problems again.
No pointy sticks? no problem. I just punch you in the head until you are unconscious and then suffocate or choke you until dead or brain damaged.
The point is if you don't want people killing other people you have to fix the people and not just some of the people all of them. If I want to kill you its partially my doing and partially yours for giving me reasons I feel killing you are justified enough to go through with it.
(What can I say I am a sick sick person and I have had a lot of free time lately to ponder on the potential methods of how to knock someone off which of course is the easy part. The not getting caught part is the harder part I am still working on.)