If you rent this DVD then watch the interview with the director on the special features as well as watching the movie. Essentially this film was made by a guy who had never had any interest in cinema until one day in some sort of mid-life crisis he decides to leave his job and invest his savings in making a horror movie, despite having no film making experience whatsoever.
Why a nail gun massacre? - because he liked Texas Chainsaw Massacre and thought a nail-gun version would be nice: "how hard could it be to make a movie?" he asks in the special features interview. Well, it turned out to be much harder than he thought. My favourite bit is the point during production that he realises that his film is never going to scare anyone and so he tries to make it into a cult classic instead.
Bizarrely he succeeds almost by accident in making a film so bad that it does in fact gain some cult status first in Europe and then in America. The sad part is that in his naivety he has signed away all his rights to an unscrupulous film distributor so that in the end he never sees a penny for all his efforts.