It's all about what level of risk your organization is willing to accept. Flight test is a great risk reduction technique, but there are many more ways to manage risk...acceptance being one of them.
With guns, you primarily need to be concerned with arcs of fire and what happens to spent links and casings. Keeping those arcs clear of the rotor blades can be a challenge, especially if the tactics require manoeuvring.
With missiles or rockets, there are many more concerns. Stores clearance testing throughout the envelope is important, but can be expensive. Good ideas provided so far with the build up, but without good data gathering (especially high speed video), you won't have any knowledge of what may occur during the next step. Start with dropping inert missiles, if the release is good (defined by ???), then continue to training rounds. Live rounds may not be required, but the first one has to be fired at some point.
If you don't have sufficient resources to fully clear the weapons, then consider clearing a very limited envelope that allows only very specific delivery methods. You reduce the technical risk, but may increase operational risk.
Also, see if anyone else has cleared same/similiar weapons on similiar types. A good place to start is to join SETP and review the papers. Also a good place to make contacts.
Can you provide details here on the aircraft and weapons types you're working with?