I worked as a trap boy for 4 years at one of quebecs largest shooting clubs. And the rule is simple if your not shooting the gun is open. I fully support this rule as well. WHY?
On day I was working as a trap boy and this hot shot closed his gun, I had a full squad and never noticed, we were shooting skeet and we changed stations his foot twisted of the cement because the grass was lower than the cement and his gun went off. Well it was pointed down, but the 7.5 bird shoot bounced off the cement and he shot himself in the balls
I never found out what happen, but there was a lot of blood
So sine that day GUN OPEN until your turn
Even where people close up their guns before their turn, I've never seen it being acceptable to change stations with a shell in the gun, or the action closed. When moving guns are to always be open and empty.