Whoever pulled trigger is responsible. When someone hand you a firearm, you just don't assume it is unloaded.
. It wasn't a gun range. It was a movie set.
Neither is a gun store counter, my living room nor the pheasant fields. I'd still place the burden on a person handling a firearm to personally check the chamber.
Baldwin has been in a lot of action films and I simply won't believe he hasn't had a lot of firearm training for them, whether low budget movies or not. Even if he hadn't, I'd still not give him a pass just because it was someone else's "job" to clear a chamber.