Plot hole (SPOILERS)
Overall good movie, but a few plot-holes. The most obvious: One man to return 2 time machines to 2000. Leaving one behind in 1946 would be the worst thing they could have done if really wanting to bury the technology.
Shooting himself was a mistake. By so doing he denied Grace a husband in his alternate time-line. Why not simply tell his father - "you go first"?