Why would you not use a straight out of the box gun?
Most of the pistol carbines I have shot were "rough" when they were brand new. There is a reason they are inexpensive.
The sights are usually pretty utilitarian. If you are not able to shoot 3 shots at 50 yards and cover it with a quarter, both the gun and you are gonna need some work.
Shot distance / shot placement are CRITICAL.
Like several have said, forget the FMJ and go with hollow points.
Shoot behind the ear AND ONLY WHEN THEY ARE QUARTERING AWAY.
50 yards is the max distance we use the 9's.
I would bet 75, maybe 80 is what a .40's usable distance is.