For a mere £395 ($670) you can get yourself a life-size laser rifle from Fallout 3. It's the Wazer Wifle, a unique version of the AER9 rifle, remade using wood and fiberglass by the talented Thomas Hughes.
Doing crit damage with it would probably be more difficult, but apart from that it's basically the same as the one in the game:
Here's how it was built:
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