When his house burns down towards the end not only is it clearly not the same building seen earlier in the film but it also is obviously not a real house, merely a frame set up on blocks with no foundation.
During the flipping car scene you can see the door open and the roll cage is visible.
Billy claims he learned to shoot from the best, this implies that Tucker taught him. However, later in the film Billy says he never knew his dad, plus his whole story in the movie is to prevent Tucker from being murdered (which seemed to happen before he was born). So who taught Billy to shoot? The only other option is Marion, but she's only seen using a gun once throughout the movie.
During one of the scenes where David flips the pistol and puts it in the holster a stunt man had to step in. You can see instead of a street with a building in the back ground you see the bottom of a shipping container and a dirt ground in place of the sidewalk. Also David had to hold the pistol with the blanks because the one used to spin was a prop made to make the move easier. David put the pistol in his pants and it went off. During the movie you can see him limp where the blanks burned him.