you could have a working magazine, like the one i used in my Kalashnikov[phun only].
also, tracers will prove useless, as the gun fires too fast. tracers will make it to look it is not working.
i built an multimode weapon on my class(mostly at getting new classmates to get used to lego technic), shooting in semi auto or 3 round burst(with less power), controlled by the use of 2 triggers. the bad thing is that it was rubberband-powered.
also, two things about the part errors:
1- there is no lego technic part with an even aumount of holes to attach connector pegs on
2- the lego technic springs actually have the springs OUTSIDE of the spring's frame.
i've did something similar before... the difference between our models is that your springs have a much smaller length(several orders of magnitude), and my model uses lasers to start the spring reactio(you could also use killers)...
not THAT new, but still original. 9/10(used stabilizers)
only copyright allowed would be CreativeCommons 3.0 - which was phunbox1's default. according to CC3, something like that is allowed, but you'll need to credit the author if you create something based off/using it