Here is the thread where the initial !!Science!! on whether bolt weight made an impact on their lethality - [Dwarven Research: The Effect of Bolt Weight on Crossbow Performance](http://www.bay12forums.com/smf/index.php?topic=115683.0)

The results were converted on reddit into a LaTeX PDF, which is excellent reading - http://dl.dropbox.com/u/2891221/DF%20study.pdf

This led to the follow up: A Comparison Study on the Effectiveness of Bolts vs Armors

LaTeX - http://dl.dropbox.com/u/2891221/DF%20study%202.pdf

Thread - http://www.bay12forums.com/smf/index.php?topic=116151.0