Well if you spray as ever you just run out of bb's in a heartbeat.
I tend to go out of at least 8 mags (80 rounds each)
For a good 3-4 hour war.
So I'm not spraying as much as other people.
I could use two if I wanted, its just generally my job to keep people in their holes, do crazy strafe runs, or flank a positon so :-/
The shaking thing isn't a big deal I'm talking about just not taking time to shoot, don't have the mentality that you have to just machine gun your rifle.
Take a shot that counts and actually get someone important out, especially something like LMGs, or Nade launchers.
I roll a P90 and I'm my squad's front/flank man, my Bro is the battle mechanic (everything needed in case a gun breaks down) and support with a LMG.