The double-barreled cannon was built in 1862 by John Gilleland in the Athens Steam Company in Athens, Georgia. It fired two six-pound balls that were connected with a chain. Being a technical half-baked failure there were no casualties as it never saw battle, however a cow was killed during a test firing. Being used as signal gun in Athens it is still there, standing on the front lawn of the Athens City Hall.
Edit - There were quite a variety of answers to this question.
The first part of the question asked who made the cannon. That could be interpreted to mean either the inventor, John Gilleland, or that factory where it was manufactured, the Athens Steam Company, which was later renamed the Athens Foundry. I'll accept any of these answers.
The second part asked about the ammunition. I think the essential point is that it fired two balls connected by a chain. I don't care about the size of the balls, but players would have had to mention the chain to get credit for a correct response.
The third part asked about the number of casualties. Sources have been presented indicating that the correct answer is zero (human casualties), one (cow), two or three (spectators), five (one Yankee lieutenant killed and four wounded), or three (one killed and two wounded at the Battle of Jack's Creek). I will accept any of these answers.
The fourth part asked about the current location. The correct answer is Athens, GA. If players wanted to specify the location more precisely, that was fine, but I couldn't give credit for any answer that didn't mention Athens, GA.
Hoosier