I don't think that people should be shooting super weapons at an indoor range. Lots of indoor ranges don't allow them. but, that's my opinion, and irrelevant to the discussion.
You did what Jesus would want you to do, you put yourself and your plans secondary to his, and honestly, you didn't have to. You could have stood on the fact that you were there first, and until you were finished, he could cool his heels somewhere quiet.
Instead of giving you the same courtesy, treating you as if you also had a right to breath the air he was using, he chose the low road, and worked you over.
your guy was obviously a hater of some sort. Hates big guns, hates this, hates that, and gee, you not only aren't one of his peeps, you also annoyed him. So, he struck out and tried to cause you annoyance.
I was sitting in a park once, smoking a cigar, reading a book, and taking in the sun. The air was pretty still, but to my back. people came and took a picnic table about 50 feet away. Out of maybe 10 available, they chose the one closest to me. Not long after, they started loudly mouthing about my cigar. since they were actually upwind, there was no way they were even possibly inconvenienced, but they just wanted to make trouble.
If I had my sony, I'd have plugged myself in and listened to some bach, and ignored their whining and grumbling. Instead, I moved another 50 - 100 feet away, so I didn't have to listen.
I let those fools win, and reinforced their bad behavior, and encouraged them to do it again. I am ashamed for that. But, I was able to enjoy the rest of a fine $9 churchill. I shouldn't have had to fight for that right to go out in the middle of nowhere and smoke a cigar and read a book without some fool coming and molesting me, but that is the way humanity works.
Some people are worse than pigs.