I know the government has used remote viewing as an intelligence gathering method, but what have they used astral projection for? Also, is it possible to harness negative entities from the astral world and use them as a weapon that can effect our reality?
Nope. If you use negative energy to hurt people in the astral it'll just get bounced back at you, from what I gather.
And the government, when desperate for intelligence solutions in the Cold War, researched remote viewing as an intelligence gathering method but I doubt they ever mastered or used it.