An answer to this question about gunpowder in the Star Wars universe includes the following quote saying that the shot from a slug thrower is not completely deflectable by a lightsaber. This seems to be listed as an advantage (over blasters) against lightsabers and Jedi:
For example, during the days of the Galactic Republic, mercenaries fearing an intervention by Jedi Knights used rapid-fire slugthrowers that were impossible to completely deflect, unlike blaster bolts.
This doesn't make much sense though. A slug, while maybe not as deflectable should be just as ineffective against a lightsaber as a blaster shot is, due to the nature of a lightsaber blade. That is, a blade made of plasma should simply vaporize the slug, should the slug manage to penetrate the containment field.
The weapon consisted of a blade of pure plasma emitted from the hilt and suspended in a force containment field. The field contained the immense heat of the plasma, protecting the wielder, and allowed the blade to keep its shape.
While a slug would seem to be more accurate than a blaster bolt (at least when used by a skilled marksman), I can't imagine that the slug would be faster than a bolt. Or if it is faster I wouldn't imagine it would be so fast that a Jedi would be unable to react with enough speed to block it, either with their saber or with the force. So what is the implied advantage of a slug thrower, versus a blaster, when used against a Jedi?