I saw this movie on early 90, I remember this segment, which I believe to be the beginning: This guy wins a aim sight on his birthday(I guess), then a scene with him practicing, he is at home watching tv at home with his family, he leaves the tv room, he comes back and shot his family (father,mother and brother).
Thanks for the help.
Very similar things happen in…
https://www.imdb.com/title/tt0063671/?ref_=tt_urv