I purchased a KHW M4 which had a problem with the bolt. When I contacted them they told me how to fix the problem, which made it worse. I sent the gun back to them (with all the parts) and they told me their recommended modification voided the warranty and they would not fix the gun. Add to this they did not (nor ever did) return any of the other parts other than the nonfunctional gun. After about I year I gave up calling the purchase a total loss.