Murder has generally always been illegal, yet it hasn't stopped murders from happening. Making new gun laws about how many bullets you get from your military service or how you can transport them won't stop criminals from using them to commit further crimes.
As someone else pointed out, you can still buy ammunition in Switzerland. There's plenty of access to guns. The difference is absolutely one of culture, which is what my point was.
Well, yeah. Most non-murderers don't murder, too.