Han Solo supposedly illegally modified his blaster. I can't find a reference on the web for this. If he did, how did he modify it and why was it illegal to do so?
Star Wars Wikia reports on its entry for the DL-44, the first blaster we see Solo using:
The DL-44 was the weapon of choice of the General and Alliance hero, once-smuggler Han Solo, who removed the barrel-sight to facilitate his fast-draw, something that the empire deemed to be an illegal modification of a blaster. In a later era, Jaden Korr, Rosh Penin and other New Jedi Order students carried DL-44 pistols when on missions where a blaster might be neccessary. Mara Jade was also known to carry one of those on occasion. They were also the anti-infantry sidearm of choice for the Rebel vanguards, in addition to their anti-vehicle weaponry.
I recall that he had an encounter with a large lizard-like person in one of the Han Solo Trilogy books, which preceded the original Star Wars trilogy. He tried to draw his blaster, but the barrel sight caught in the holster, leaving him in a bad spot. I think this was after he had freed Chewbacca, who came to his rescue, and it was this point that they became partners.
Shortly after this incident Han took some time to remove the sight from his blaster, to avoid a similar situation happening again.