Mark,
This sort of thing is a very emotive situation.
With "the guy" trying to break into you van and your livelihood.
I would feel the same to be honest, but to aim a loaded firearm at another human being in civillian life?.
I've been a hunter for over 20 years and I could never shoot a fellow human being.
I have 2 shotguns and 8 rifles here, unless I was directly threatened inside my house here wouldn't I even think of loading a rifle or shotgun.
Under current NZ law you have to keep your rifle, ammo, the bolt and the magazine in 4 different places within your residence.
The Police here check you here every 6 months.
That is if you have a gun licence.