I'm going to have to agree with the first reply here, sorry.
It's quite possible to hit things with the blaster on hard/very hard.
If the stormtroopers keep running back and forth to avoid getting hit, which I guess is your problem, aim ahead of them. Lead your targets and KEEP MOVING all the time to avoid getting hit. With practice you'll be able to judge how far ahead you need to aim, and then you should be fine.