I have a UNV 20ir illuminator for use with a digital night vision scope. From the reviews I've read, most people speak very highly of this product. However, I am having issues with mine. The first light I purchased would not stay lit once it was turned on. I sent it back to UNV and they replaced it with a new light. Now the light turns off, once I fire the first round. I've tried tightening the battery cap, and this did not help. I'm shooting an AR-15 6.8 spc. Has anyone else had similar problems? If so, is there something simple that I'm missing here?