Bill's requires you to voluntarily show your form 1/4 to them prior to shooting it. It's been that way for at least the last 10 years. Basically, they don't want to be known as the place that turns a blind eye to someone commiting a felony. That invites additional BATFE scrutiny. I'm sure that it would also cause problems with their insurance and license with the city council.
The only people who can *legally* compel you to show them your form 1/4 is a BATFE or IRS agent (since it's a tax document), or a judge. Law enforcement cannot legally compel you to show them your paperwork. That being said, it is against the law to own NFA weapons unless you have registered it with BATFE. The recent change to the suppressor law in MN states that it is a felony to sell or possess a suppressor that is not lawfully possessed under federal law. Much like carrying a firearm in public is a crime, but having a permit is an exemption from committing the crime, having a suppressor is presumed to be a crime unless you can prove that it is possessed lawfully under federal law. The only way you can prove that is to voluntarily produce your registration documents. It's a bit of a catch 22 - you are not legally required to produce it for law enforcement, but if you don't you will be arrested.
https://www.revisor.mn.gov/statutes/?id=609.66Its up to the range officer at Bill's (or anywhere) to make a judgement call regarding anything they feel is unsafe or unlawful. They might give you a warning, they might ask you to leave. They go through staff fairly regularly, and how one person responds to something they saw (or thought they saw) might be different week to week. They also give the range rules to everyone before they go out to the range. It's true that there are idiots who for some reason can't seem to understand simple instructions. It's always going to happen. My observation is that guns are uncased behind the line, and muzzle sweeping occurs most often by "old timers" sighting in their rifle for hunting season. If the ROs see someone doing this, they'll address it. However, we are all individually responsible for our own safety. If you see someone doing something you feel is unsafe, politely correct them, and then notify the RO.
If anyone has a problem with a business, any business, before going off on a public rant on the internet they should contact the manager and discuss what happened. If you don't do that, you have nothing at all to bitch about. We're all human, and suffer all the failing that go along with being human. Most businesses will accommodate a reasonable complaint when contacted about it. If you don't give them the chance to make it right, or blame a business on the poor behavior of another customer without alerting them to that behavior, you're just shaking your fist at the sky.