I.e., you don't trust him with a shotgun, and should stop pretending you do.
If I didn't trust him to collect guns through legal means, I wouldn't have trusted him to collect even a single gun through legal means.
Why should it be any of my business, to indulge in anything more than idle curiosity about, what hobbies a law-abiding citizen lawfully spends his time and money on?
The Australian position on gun ownership is pretty clear: No gun ownership by default, but you can appeal to the state for an exception. Once you've made an exception, you've made an exception. I don't see any room there for "by default, we don't trust you with a gun, but we'll make an exception, but we won't trust you, but we will trust you, but we won't, but we will."
If you don't trust a man to have six shotguns, then you bloody well shouldn't have trusted him to have even one of the damn things.