They write off explanations due to wind resistance as too small to consider, yet the x-ray showing the same depth of bullet depth is fobbed off.
As several people have asked, I would like to see this with a much longer beam, with the gun aimed at the very end.
I know from sailing that you lose a lot of speed if the sail is flapping around and spilling wind, it could be that the block fired from its centre builds up a cushion of air above it that slows its ascent ?
It would be interesting to see a baby version in a vacuum . Perhaps a nice experiment for NASA ( or China ) to do on the next moon trip :-)