Today I had nothing to do, so I got some mousetraps and modified your design. It is very very basic at the moment, but it provides enough to test with. My theory turned out to be right, and if angled correctly, can achieve possibly 10ft...rat traps would probably add another 5 feet if i used rat traps. Maybe ill get some pics up for you to see.
I'm definitely looking forward to seeing this so i can make a few of my own. I'm part of a team that participates in HvZ at my university, and there have been many times that we were rushed by "zombies" and could really have used something like this to thin their numbers quickly and cause confusion as to who had been hit.
How expensive exactly are mousetraps, and do you think I could simply use toilet roll springs, with a piece of cloth suspended between the halves of the pencil case? I'd just prefer avoiding something capable of removing my fingers.
Edit: So I realize how you expect to use mousetraps now, but I'd be afraid of the spring on the trap being to powerful to the point that it would break the pencil case very easily. I did, however, find some really cheap torsion springs: http://www.rochfords...1_A_promoid_E_5