Being experienced in aircraft structural repairs, I can attest to the muscle a 9X rivet gun has.
I would actually send it back to Gun Vault. But, instead of a "love" letter, I would provide a full detailed report from day one of your troubles. Copy this thread and send it as well. Be sure to keep your emotions in check in the writing and stick with the facts in your problems. I have done this with products in the past (not necessarily firearms related items) and I've received everything from "Too bad, so sad" to product replacements with discount coupons for future purchases.