I have a 3/17 Utx85 that I have been using for since I bought it. Yesterday it's has decided to stop locking up in the open position. When it fires it just falls back in to the handle. If I pull it out to lock, it will fire as many times as I want. However if I let it sit for 10 minutes, it does it all over again. Is there something I can do? Or do I have to send it back. Thanks in advance, Steve.