DAD of 17 Donald Ewers pointed a handgun at two Mormon missionaries who visited his home.
He brandished the replica weapon after an initially friendly chat with the two young men, Gloucester Crown Court heard.
Judge Jamie Tabor said: "When someone has a gun pointed at them, whether it's real or they believe it to be real, or not, it has a devastating impact."
He told Ewers, 47, it was a "frightening and irrational act" with no obvious motive.
Ewers, of Cromwell Street, who has children aged from seven months to 32 years, admitted possessing an imitation firearm with intent to cause fear of violence.
Prosecutor Lisa Hennessy said missionaries Paulus Chardon and Cameron Kramer visited Ewers' home on December 19 last year on the expectation of finding someone called Roger.
Instead, she said, they found Ewers at home.
They left him a Book of Mormon and all seemed very pleasant.
But Ewers suddenly started to rummage under his duvet and produced the imitation weapon, before saying: "Don't mess around, if needed I will kill."
The missionaries discussed Olympic champion Usain Bolt and Jamaica with Ewers while he continued to point the gun towards them, Mrs Hennessy said.
They left and Ewers was later arrested.
Police found a BB handgun underneath his mattress. He denied the allegations, claiming the missionaries were racists.
Frazer Stuart, in mitigation, said alcohol was at the root of Ewers' problems. "He's at a loss to explain his behaviour and is not a violent man by any stretch of the imagination. He appears to have gone off on a tangent," he said.
Ewers was jailed for 17 months.
