From the Physics arXiv Blog:

Imagine the following scenario. The end of civilisation has occurred, zombies have taken over the Earth and all access to modern technology has ended. The few survivors suddenly need to know the value of pi and, being a mathematician, they turn to you. What do you do?

If ever you find yourself in this situation, you’ll be glad of the work of Vincent Dumoulin and Félix Thouin at the Université de Montréal in Canada. These guys have worked out how to calculate an approximate value of pi using the distribution of pellets from a Mossberg 500 pump-action shotgun, which they assume would be widely available in the event of a zombie apocalypse.

Full how-to details at the link, if you’re really interested. Here’s my 500, and my calculator. I’m guessing the calculator is easier, so I’ll just include that in my survival room.