If I were Sam, I would have disposed of the gun instantly. Guns and shooting would only give the racists another reason to hate. By getting rid of the gun, Stick would not have any temptations, and Sam's obviously troubled mind would be put at ease. It was clear that when Sam found the gun, he was absolutely horrified. Even if Stick would be angry, the good of disposing of a dangerous weapon would outweigh Stick's frustration.