According to this (
http://www.lectlaw.com/def/d011.htm) that isn't correct. The legal crux is in both the use and the intent of the user. Design intent is neither a necessary nor sufficient condition for something to be a weapon.
I have firearms that were admittedly designed as weapons (very good for turning dollars into noise and flash (or optionally little noise and no flash)). Olympic grade target rifles can hardly be said to be designed as weapons.
What firearms are (hopefully) are precision projectile throwers. It's the target that makes them weapons.
Okinawan rice flails in the hands of a peasant are a farm tool. In the hands of a karate practioner it could be used as a weapon (nunchaku). Katana swords in Japan today are objects of art for most owners. For an Iaido practioner a sword could be a weapon. But for most of us having one is an accident waiting to happen.
Having a piano doesn't make one a musician. Having a power projecting tool doesn't make one armed. It's a popular saying around here, but it really is the software, not the hardware.