Automatic weapons take a penalty as though you were making a full attack (generally -4).
Blast weapons take a -2 penalty to hit.
Line weapons nd grenades don't take any penalties to hit at all.
Right. Note that some of the projectile blast weapons are not unwieldy, so they can full attack at -6 total penalty (or -4 if you have a bipod/gunners harness).
Grenades, unlike line weapons, can take range penalties, of course. But they don't have any inherent penalties, same for Explode weapons.
And, of course, any to hit penalties on explode weapons double as penalties to their save DC (which is really the only reason I see not to deadly aim with them.)