When Walter returns the gun he took away from Clay to his mother, she justifies giving it to him as a remembrance of his dead father, and she says "Of course I didn't give him any bullets."
So, how come he managed to get the bullets for the shooting?
I thought this was a flaw, although I liked the film.
This is a rather late answer, but better late than never, I guess...
Linda asked Walter to take care of the gun for her, so that she didn't have to get rid of it. Then when Walter went to see the man who he thought killed his sister, he brought the gun with him to shoot the man. So I suppose he's the one who loaded it, and when he returned it to Linda it was probably still loaded. Then Clay used it!
thank you for explaining that. i just watched in on lifetime and i was angry that michelle p. still had bullets in the house.
so now i dont feel like i wasted 2 hrs. to see a stupid ending.