Police ballistic experts carried out tests which proved the makeshift firearm, which Doris claimed to have used in seven shootings, was capable of firing.
Doris favoured the "pipe gun", which is fitted with a six-inch silencer, as the unique design would make tracing its bullets to any known weapons impossible. Yesterday, he was sentenced to 13 years in prison for conspiring to murder Kevin Martin in a 30,000 contract hit.
Property developer Martin Black, who hired Doris as a bodyguard and wanted Martin killed to avoid paying him 100,000 from a soured business deal, was jailed for eight years.
Together, the pair built up an arsenal of weaponry, which also included a samurai sword, knives and a crossbow, and tried to set up ambushes to murder Martin, 38, in the Capital in July 2008.
The long sentences were today welcomed by former vice girl Claire Lizanec, who was left fearing for her life after giving evidence in court against the men.
Doris, 40, boasted to Ms Lizanec of his murder plot, but later threatened to kill her after she stole a Luger-style gun from him to sell to buy drugs then reported the conspiracy to police.
Ms Lizanec, 28, who is now in hiding, told the Evening News: "I feel safer now that they've been given long sentences and I'm thankful that it's finally over.
"Francis Doris is a bad one so you just have to say thank God that they never managed to kill the person they were after.
"My main concern is me and my children, and keeping them safe. I'm pleased that this chapter of my life is finished and I can move on."
Sentencing Doris at the High Court in Glasgow, Judge Norman Ritchie QC told him: "You were the hired hand, the hitman. You have a dreadful record, especially for crimes of violence."
The court heard Doris, 40, who showed no emotion as he was jailed, had a criminal record which included a previous nine-year jail term for firearms offences. Sentencing 33-year-old Black, Judge Ritchie said the former 175-an-hour business consultant had enjoyed a "respectable background" and "comfortable lifestyle", but had fallen in with "dubious characters" before "taking up with Francis Doris and hatching a plan to kill Kevin Martin".
Sentences were reduced by two years because of time already spent in custody.
Ms Lizanec met Doris and Black in a Leith Walk pub, and returned with them to Black's Colinton Road flat where she and Doris smoked crack together. There Doris – who often signed off his text messages "Murder Inc" – showed her the collection of firearms and boasted of his contract to Martin. He claimed he had "shot at 11 people and hit seven" with his "pipe gun".
She spent much of the next few days with the two men, even sitting with them in a Mercedes as they waited for Mr Martin's arrival at a city hotel where he would be attacked.
But Ms Lizanec later told police and armed officers swooped on Black's flat and arrested the pair.