It would be better if you just hooked up the solar panel directly to the charger. You waste a lot going from DC (solar) to AC (inverter) and then back to DC (power brick).

Here is a video of someone else bump firing. No skill, no accuracy, not impressive.

http://www.youtube.com/watch?v=MydCuTfgt0k

I don't think its modified. It is called "bump firing" where you use the recoil of the gun to fire the next shot on a semi-auto gun. It is wildly inaccurate.

http://en.wikipedia.org/wiki/Bump_fire