MythBusters Episode 51: Myths Reopened

SPINOFF: A hybrid rocket can be propelled with salami. (From episode 40)

confirmed

Salami, like the paraffin used in the first test, was able to propel the rocket, although it tended to explode instead of providing even thrust.

(This myth was revisited and confirmed again in More Myths Revisited.)

REVISITED: An wooden arrow can be split in half through a direct hit in the tail by another arrow. (From episode 36)

re-busted

Even after multiple direct hits on a solid wood arrow with the bone nock removed, a tail-to-tip split could not be achieved. It took an arrow made of hollow bamboo to create the splitting effect seen in the movie. Because with a normal arrow, the second arrow will follow the grain, which will lead to the side before it makes it to the end. Also their tests revealed that an arrow fired from a traditional bow wobbles in the air enough that it won’t hit the end of the arrow straight.

SPINOFF: A modern firearm can be fired if completely submerged in water. (From episode 34)

confirmed

All of the firearms (a 9mm, a .357, a 12-gauge shotgun, and a .30-06) were able to discharge underwater, however the bullets lose velocity rapidly and are rendered less than lethal beyond a meter. (The entire gun had to be completely submerged in water – all pockets of air must be removed – in order to prevent a possible explosion when fired.) Furthermore, the break-barrel shotgun (albeit a relatively old and un-modern design) destroyed itself when fired underwater. Finally, the water pressure might cause the spent cartridge to fail to leave the chamber and, hence, effectively reduce the gun to a one-shot deal. A revolver would not have this problem as they do not eject their spent cartridges after each shot.