Knives, nunchucks, brass knuckles, etc. are usually covered by state level laws, from what I've seen, and the legality varies widely. Firearms are a slightly different story, since the 2nd Amendment very specifically protects firearms ownership. So yes, it is possible that somewhere or other, a switch blade knife is illegal while an "assault rifle" is legal.
I saw "assault rifle" in quotes, because most people talking about these issues have no clue what an "assault rifle" really is, and are repeating garbage they heard from various anti-gun activist groups, who routinely use a totally bogus definition of "assault rifle" or "assault weapon". It's important to understand that owning a real assault rifle (that is, one capable of select-fire / bust-mode / fully automatic operation) IS legal but it's VERY highly regulated, VERY expensive, and you can only - as a civilian - purchase weapons manufactured before 1986.
I saw "assault rifle" in quotes, because most people talking about these issues have no clue what an "assault rifle" really is, and are repeating garbage they heard from various anti-gun activist groups, who routinely use a totally bogus definition of "assault rifle" or "assault weapon". It's important to understand that owning a real assault rifle (that is, one capable of select-fire / bust-mode / fully automatic operation) IS legal but it's VERY highly regulated, VERY expensive, and you can only - as a civilian - purchase weapons manufactured before 1986.