In the 'cosmological' sense, What was the mass of the bullet? Who fired it? What kind of gun was used?
Reproducable same results with many bullets from a 9mm and 40 cal. There are probably others by now.
http://www.youtube.com/watch?v=_57GbWN1G1w
9mm
http://www.youtube.com/watch?v=0h3MBNpQHS0&NR=1
http://www.youtube.com/watch?v=BPs70mhEM_A&NR=1
40 cal
http://www.youtube.com/watch?v=MC_5a0lNDv0&feature=related
http://www.youtube.com/watch?v=foZlciP6gUQ&feature=related
This is also interesting.
http://www.youtube.com/watch?v=M5xVPJUdTHk&NR=1