So my father who lives in the middle of nowhere and owns an old hunting rifle, shotgun, and a few pistols - locked up in a safe, probably untouched for a few years - is "extreme"?
It's not just a matter of what a person does themselves; it's a matter what what they advocate for.
For instance, if your father advocates for, say, the general right to carry a concealed pistol in a mall, I would say that he's extreme regardless of whether he exercises this right himself.
... but as it stands now, I don't know whether your father is a gun extremist or not.
If anything is extreme, it's the level of emotion elicited by these inanimate objects.
For me, it's not the inanimate objects that elicit the emotion; it's their death toll.
Firearms kill about as many people as car crashes in your country. I've dedicated most of my working life to reducing deaths and injuries from collisions; if anything, my response to guns has been disproportionately lax.