Not all blasters are powered by crystals it could also be powered by liquid or gas for the medium, a good portion of blasters use Tibanna Gas as the favored medium. I wouldn't say Stormtroopers were bad shots though, I mean they did kill all those Rebels aboard the Tantive IV, granted close range yes but Boba too was at a fairly close range.
Besides if Stormtroopers were such bad shots, then I doubt the Rebels wouldn't have lost every engagement they were in.
well it was a small hallway so all they had to was fire straight and even then they miss A LOT. Not to mention C-3po and R2D2 walk right down that hallway completely unharmed.