IIRC (1) Those guns are all bulky rifle-style things which are great when you're defending against an invading army but not so useful when you want to shoot some of your classmates, and (2) There are lots of guns around but access to ammunition is tightly controlled.

Even thought I live there I only have a limited understanding. But from what I can tell a) ammunition is sold over the counter to everyone with a license. b) you are talking about the military rifle. Which is by far not the only gun you can buy (again I don't know the exact limits, I assume automatic is somewhat banned)

You have an article in the wikipedia that informs you that (1) is false, they can buy semi-auto freely. And (2) is also false, they can buy ammo if they legally own a weapon.

The difference is in the quality of the society.