He then explained matter-of-factly that it would do the same thing to a human, and that they would be permamently dead, so unless that is REALLY what needed to happen, not to use it. He then told me where it was kept, and that it was kept loaded and was not to be viewed as a toy. I could use it whenever I wanted, but only with adult supervision.
This actually worked rather well for two reasons. It wasn't forbidden, so I didn't feel a need to mess with the guns just to break the rules. He also specifically chose the shotgun, which has some insane kickback even if you are a fully-grown adult male, and it REALLY HURT when I used it.
I think gun locks are a bad idea for kids over about 5 or 6 because they WILL be able to find the key and unlock it. Just like they know where the Christmas presents are hidden and everything else that the parents think they have hidden from them.
At the age of 8 most kids are capable of understanding things like death, unless the parents have let them be too sheltered. They should have had a pet or two die already, perhaps a grandparent or other older relative, and older people they know through church or the like. I was well aware of the idea of death and that it is permament by that age.
On the flipside, I do recall my dad not liking Doom, and I was around 12 or so then, and didn't want me to play it. Games like that can desensitize people to violence in general, which doesn't go well with an unwillingness in American middle-class society to openly talk about death or experience it at a personal level. People try to insulate their kids from it, but they really shouldn't.