Some great pieces of advice and common sense in the thread.
Re. holding the barrel, I was with a school group once when I told them this and the teacher put his hand up and said. "Otherwise you might end up with a permanent scar like this!". The skin between his thumb and first finger had been sliced by an air rifle during loading when he was at school as a child.
The follow on is that the Centre he was at took him off to the local hospital. The school was informed and the school sent a message to his Mother who was at work. Rather than being told her son had had his hand trapped and had gone to casualty. Mum was informed that her son had been involved in a firearm's incident and had been taken to A+E. The same message but this version sounded a little more urgent. His mother got a speeding ticket !!!