Who’s his dad a gunsmith for? I thought Australians weren’t allowed to own guns.
That's a myth - while Australia does have some fairly restrictive laws on guns (universal licencing and registration among them) Australians can certainly own firearms - and a large number do.
Basically you have to have the right licence for your weapons, and while it's quite easy to get a licence for a basic longarm, semi-automatics and hand guns require higher level licences, which though they are obtainable, take more effort to acquire. A fully automatic licence is possible, but difficult to get.