One thing...Please let's just call it magic and not science :)
We have witches after all we don't need to back it up.

Generate a fair amount of electricity... Understatement!

Your shooting coins like bullets, and essentially have a literal 'hand gun'.
Let's not try say it's science, it's magic.
Your fingers are not ferromagnetic so your outright creating your own magnetic fields. 

Other things to consider and reasons it's not a mainstream weapon.
Theres a high force that is also pushing the rails apart. 
The power source and requirement is pretty [b]huge[/b].
The rails generally only survive a couple of shots due to the large amount of heat in the short circuited layout. Plasma and corrosion damage.

So don't try it with your home power supply coz your just gonna trip your breakers.

But concept is cool. 


But thats me for the night, interested to see where things are when I wake up in the morning.  XD 

NIGHT ALL