Q:

Was the vertical cannonshot related by Samuel Rowbotham ever performed?

A common claim in support of "Flat Earth" models is that a cannonball fired precisely vertically drops back upon the cannon, even back down the muzzle. One such claim appears here http://www.atlanteanconspiracy.com/ 
These claims clearly echo the 19th century one reproduced here in Samuel Rowbotham's "Zetetic Astronomy":
http://www.sacred-texts.com/earth/za/za21.htm#page_67
Although it's clearly claimed that the experiment was performed, the stated consistency of the shots (maximum sideways variation of 2 feet in a 28 second flight) seems implausible, at least given the popular understanding of smooth-bore cannon accuracy and possible effects of wind and cannonball spin. Is there any corroborating evidence for the experiment as reported, or for subsequent enactments of it?

A:

Yes, the experiment was done, but much earlier.  
See Vertical Projection in a Resisting Medium: Reflections on Observations of Mersenne The American Mathematical Monthly Vol. 121, (2014), pp. 499-505

Mersenne began carrying out experiments with vertically launched projectiles in the 1630s.  

Also, Rene Descarte wrote to Mersenne in 1636:

Thank you for the account of the ball shot vertically that
  doesn’t drop back; it is very remarkable

and in 1638

There is also the observation [mentioned on page 29] that you
  told me you have made yourself, and that other writers have
  described, namely that cannon balls that are shot straight
  up don’t fall down again.

and Descarte was in 1634 the one who suggested the experiment in the first place:

Also: you told me in a previous
  letter that some people you knew could help to perform the
  experiments that I wanted done; so let me tell you about an
  experiment that was published not long ago in Leurechon’s
  Mathematical Games. It involves a large cannon placed on
  flat ground, pointing straight up at the sky, and fired. I
  would like this experiment performed by people who are
  interested and have the means. The author of the book says
  that the experiment has already been performed many times,
  and the cannon-ball didn’t once fall back to the ground.
  Many might think this quite incredible, but I don’t judge it to
  be impossible, and I think it’s well worth looking into. 

