Character mistake: The information on Walter's "patient information sheet" lists his address as 5962 Delco St but numerous shots indicate his house number is 238. (01:03:25)
Character mistake: When Walt is fixing the washing machine in the basement, he adjusts the wrong corner of it to stop it from wobbling.
Answer: Well, a lot of veterans actually buy their weapons once they have retired, since they have the constitutional right to keep and bear those weapons. However, I don't think it is said in the movie that those arms were exactly the ones Kowalsky used during the war.
Actually, yes he did say that it was the one he carried. When Tao asked what it was like to kill a man, Walt says I shot the kid in the face with that rifle you were holding earlier.