@Sabato - reading the core rules carefully: I think you can combine tracer rounds and vision magnification in order to shoot from extreme range with -1 penalty.
You just cannot do so that often as you need to first take aim, and then use full auto in a complex action. But since you have time - I suggest you do so if you have tracer rounds as that way you will not need to wait for the biker to get close. (It may take the biker quite a few combat rounds to get close.)
Now the fun part is that the take aim negates the -1 penalty, as it increases the dice pool and maximum accuracy. I think I read that you can take aim until you get a bonus equal to your willpower. (super awesome especially for the accuracy that is also improved by take aim)
Since you have a combat round or two until the biker is in range, I'd prepare that shot from now. With some dice luck you'll one shot that biker.
PS: I actually learn quite a lot about the mechanics from these discussions this is by far the most complex game I ever played