I'm a serviceman in the Ukrainian army. After shooting during deployment I didn't get a chance to clean my rifle and went to the hospital. After I returned this thing at the end of the barrel got rusty and I can't unscrew it. There are no appropriate tools here, we're in the field. How do I fix it? My mates suggested to put that nozzle into a cup with coke, it's supposed to remove the rust. Is it legit?