In order to inflict damage, you need
1) "Physically" hit the target with the projectile. The projectile's rectangle must collide with the target's rectangle in the game world.
2) Then you get an attack roll. Based on your + To Hit and the enemy AC, there is a certain chance to hit. The game rolls from 0 to 1 and if it rolls less than that chance, you hit.
3) Then you get a damage roll, i. e. 3d5 + 8 for the pistol and 4d5 + 12 for the rifle. Then, your enemy gets a series of rolls for resistance. (It works like this: they roll against a certain chance, and if they are lucky, the damage is cut to 1/2 and they can roll again. This continues until the damage is cut to 1/16 or they fail the roll.)
The only advantage of blasters over other missile weapons is, as correctly stated by Peter, that they inflict energy damage and there's no resistance against that. That only means you can be sure that if you make it to the step 3), what you roll is what the enemy gets, without any reductions.
(Of course, their other advantage is a very short recovery time, but that works the same way as in all the other missile weapons.)