What I was taught about a slow fire (or no fire) is to keep the weapon pointed down range at least 30 seconds, up to a minute if you want. At that point you can be fairly certain that it won't fire. Place it where you can keep track of it, and on the way out, give it to the people at the range, and tell them what happened with it. More than likely they will either disassemble it, or drop it into another gun and try to get it to fire.
"I don't have to like it, I just have to do it."