As for the safety concern, you are right to voice but I can assure it's just like any airsoft gun, if used properly it should be fine. All of the nails that are used (two safety pins and a trigger pin) have the ends filed down so they are very very dull. The two safety pins haven't shot out yet after dozens of trials and if for some weird reason they decided do, they'd be no more hazardous than a bb. As for the trigger pin, let me explain. I use fishing line for the trip line. It has a certain amount of elasticity to it, and I'm not sure if it's the tension of the line that shoots out the pin or the CO2 force, but the trigger pin will "shoot" a bit. In that particular video it hit my arm and gave me a little scratch, so always wear glasses, but otherwise again, no worries.
The yank in the video is excessive. The more power the trigger pin is removed with, the sure...er.. (that seems weird) you are of having a clean detonation. However, I've also done tests of slowly walking through the line, and due to the elastic feature of fishing line, the trigger pin is still yanked out when the tension is too great, so it works well like that too.
BB's and Firing Direction:
If you wanted to use powder, but have it shoot AT you I could always redesign the barrel so it has a 90 degree angle at the end so it shoots towards your ankles rather than up.
For bb's, the 90 degree might work if it was a gradual curve to 90, but something tells me this would be tough.
I think though, that with some creativity, and maybe an extra nail or two you can make the mine detonate and shoot in almost any direction. But yeah, as was mentioned, a few more days on the work bench could change a lot so thanks for the comments/ideas and keep 'em coming.
Oh, someone also said "if it's easy to use". Yes, it is very easy, but here's the other bonus. For fun when I made them I made an operating manual, which is actually pretty thorough. Goes over deployment, mechanics of the mine, troubleshooting etc. So that idea is out there too.
As for spring talk, thanks a lot, anything helps. Feel free to PM or e-mail.
Lastly, I'm also working on getting some more video/photos so I'll try to do that asap.
"To invent, you need a good imagination and a pile of junk." - Edison