His tanks are definitely capable of shooting at least blank rounds. They do it weekly at the museum. I would not be surprised if they can shoot the actual live munition without issues if you can get hands on it.
It's also legal to equip them with machine guns, as long as the gun's transferable under the Hughes Amendment. An M2 Browning would set one back $20K or so.[1] But a guy like Paul Allen could splurge and get a GE M134 chain gun for $500K.[2]
One could also equip them with explosive ordnance as long as each piece of ordnance is registered as a destructive device (along with $200 tax stamp).
These are minor obstacles to the wealthy. Gun control is for the poor.
[1]: https://www.morphyauctions.com/jamesdjulia/item/lot-1009-m2-...
I can't see the pragmatism in demanding equivalence of regulation.