It's not the range's job to enforce federal firearms law. Just like it's not their job to verify you are able to legally own a gun before you shoot. They face no liability IMO for any "ATF spot checks". There is no CFR or Statute I am aware of that requires ranges to verify proper possession of NFA items. So that begs the question- if there's no law on the books requiring them to check, then why the hell are they asking?
Yea-I see your point scott. I was thinking something different, but you guys got me on this one. lol