Weapons work all types of ways.
sonic weapons work by intake air and pressure causing a sonic boom
Use silver weapons or magical weapons. Magical weapons always work, even when their charge is depleted!
Well their specialists in the use of/design of weapons, and usually they work for the government.
The US military has Special Weapons Schools where you learn how to operate, maintain, etc. nuclear weapons.
Either by gas or recoil or a combination
Default is Z and X to move between weapons, though 1-9 would work for selecting weapons too in single player
Just playing the game then trading those weapons for the weapons you want. That won't work because what if you were free to play so this may take a long time but you randomly get weapons when you play :]
Short answer: The military. Longer short answer: Weapons are sometimes designed in-house AFAIK, but in the USA weapons are also contracted out to civilian corporations for design work, I think.
The assault weapons ban worked in that it reduced the number of crimes committed with the banned guns, but it did not reduce crime overall.
Yes when you get them you can use them
The Military who might want to use the weapons systems have people called 'Weapons Assessors' who have the training and experience to do the work. These are people who do work with the Military not the Government or the Manufacturers
They are not willing to work with them because they have so many weapons.