Took me a while to find it but here is the actual code number. This is for Colorado Springs. Each city will be different.
9.7.104: DISCHARGE OF WEAPON:
A. It is unlawful for any person to wrongfully fire or discharge any cannon, gun, pistol, revolver, rifle, shotgun, air gun, BB gun, gas operated gun, spring gun, or firearm within the City. The discharge of firearms using only blank ammunition by the members of any military company when on parade or when engaged in an official ceremony, done in accord with the command of the commanding officers, shall not be deemed a violation, nor shall the discharge of firearms at shooting galleries as a licensed business, or as part of a business licensed or permitted to operate within the City be deemed a violation.
They basically got everything covered. You might be able to get away with a slingshot