Hey guys,
Using the big voice, like shooting, is an exercise of a power which is needed sometimes, and is fun to practice - but like shooting, it's something to use with restraint. If somebody sweeps me or mine at a public range, I'm going to get their attention right now - but if it's a safety violation which doesn't immediately threaten me or mine, I'm going to say something like "hey guys, sorry to bother you, but you should know that.... I'd really rather you didn't do that here, and the range officers or other shooters might... "
I think the original poster handled his situation pretty well.
One example I think I handled well was years ago, in a beginning shotgun class, when one of the other students (standing next to me) tried to sweep my face with a gun which I was pretty sure (not 100.0%) was unloaded: I grabbed the barrel so he didn't sweep me, and when he looked around to see why his gun was stuck I said something like "please don't EVER do that again."
Part of teaching is to get their attention, but another part is to get their respect.
Lots of people just don't know about safety rules, and will respond immediately if you give them even a little bit of explanation. I've got sympathy for beginners, because I was one too.