I'm still confused by what you mean by "rotary projection aperati(spindle/wheel)" in this context.
When you say "wheel", do you perhaps mean flywheel? where the energy is stored as kinectic energy in a big heavy wheel that's spinning really fast?
Or do you mean something that will be still until you pull the trigger, at which point it flings a projectile? If you mean that, I'd need to see a design, as I'm currently imagining you trying to walk around with a catapult in your arms, and that is impractical on many levels.
other than a spring, what sort of energy storage aparatus were you thinking?
Your standard spring-powered rifle is not designed to be lethal, or not to anything past small game. But that is because the spring is set by a single yank of the arm. By using gear or pulley system to crank a spring compressed, you store a greater potential energy by exerting greater movement. In other words, it takes 4 or 5 cranks of both arms, instead of the yank of just one arm. If you can find the right sort of spring (which is always a pain), you can make such a device every bit as strong as a crossbow.
One major problem in that situation is going to be one related to the conservation of momentum. As the spring changes shape (compresses or extends), it is going to cause a shift in the center of gravity of your device. If it is fast and heavy enough, it is going to kick in which ever direction the center of gravity moves, with enough force to yank the gun right out of your arms. Bows are nice because they are made of lightweight material, that overall moves fairly little.
As far as materials, it gets very complicated very quickly. You have to understand where forces are going to be applied on your design. Some portions would need to be steel, while some portions can be wood. The thickness of the steel needed, and the configuration all gets into lots of physics and engineering issues.
When talking about storing up this level of energy, it is very important to have the math right in your design, and within orders of magnitude of tolerance, or you can wind up with a part smashing through your face, and either killing you, or ruining your life.
Again, this is a good reason to not start designing "new" things until you fully understand and can build things that have stood the test of time. Often, "new" ideas aren't really new, you've just never heard of them because they don't work.