The Peacemaker Cannon was based somewhat on the design of the "Oregon" cannon which was designed by John Ericson. However the Oregon had been cast correctly and test-fired over 100 times, Interestingly The Oregon Cannon is located near the main gate of the US Naval Academy.
The President and Julia got married and had 7 kids, There was a 30-year age difference between the two of them, ... which turned heads, but it seems like they made a happy couple so I'm not going to judge.
Captain Robert Stockton, the man who designed the Peacemaker, failed to test it adequately and fired its final shot, faced no charges, and was resolved of any responsibility. He went on to captain the USS Princeton in the Mexican-American war and later became a Politician.
Sources - lots of good reads here!
Bonus Points for scrolling all the way down here - I found this old newspaper in the Library of Congress archives, talking about Capt Stockton and the Incident. (3rd Column)