Jefferson County Sheriff's Capt. Ron Arnhart said Ronnie G. Sanders was struck by shrapnel from the exploding cannon Thursday afternoon outside his house.
Sanders and two friends had been making the cannon when it somehow exploded, Arnhart said.
No one else was hurt, he said.
Arnhart said the cannon was constructed from some kind of pipe filled with black powder with a wick attached.
Sanders was declared dead at the scene after the explosion, Arnhart said.
"He goes to an outbuilding and the pipe itself disintegrated," Arnhart told the St. Louis Post-Dispatch.
Sheriff's deputies and agents with the Bureau of Alcohol, Tobacco, Firearms and Explosives investigating the cause of the blast said they believed the cannon was meant for for recreational purposes and was not illegal.
"They had done this before," Arnhart said.