I figured that for frames. Aluminum is strong but not "springy", so to speak. Never seen an Aluminum can spring back after it's been squashed. <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" />

And yes Autos are mainly made for Military/Police personnel who aren't going to spend and exorbitant amount of money on knives.

But if you say "a simple durable housing is needed" why not just plain simple stainless steel? It's cheaper, more durable (in finish mainly), and has a bit of springiness just in case. It's by no means lighter, but what kind of military/police personnel would care when their already carrying a good amount of gear. A half pound wouldn't do much at all.

Also thanks for your guys' response.