Having been shortened at both ends - reducing the length from 1.2 metres to less half a metre - the gun would have fit easily in the backpack Monis carried into the Lindt cafe.

On Wednesday, eight months after Monis held 18 people hostage and murdered one of them, his weapon was physically produced in public for the first time at the ongoing inquest into the siege.

Crime scene officer Walter Murphy held the La Salle Manufrance gun aloft, before "firing" a number of dummy cartridges to demonstrate that, despite its age, the weapon was capable of firing four shots in as little as five seconds.

The trigger clicked eerily in the courtroom, dummy cartridges thudding on the floor.

"It's in fair working order," Mr Murphy said.

"It's quite well designed, thought out … features you'd find on a better quality firearm."

Due to the alterations at both ends, the gun would have been unusually light. But as consequence it would have kicked brutally in Monis's hands.

"The recoil would be extreme because the ergonomics are compromised," Mr Murphy said. "It's very light but it slows down the time it takes to fire."

The gun was very dirty when recovered from the Lindt cafe.

There were 21 cartridges with a mix of brands and gauges in the killer's pockets and two in the firearm itself.

"It sounds like a mix of old left-over shells, yes?" counsel assisting the inquest, Jeremy Gormly later asked ballistics expert Lucas van der Walt.

"It might, yes," Mr van der Walt replied.

Five spent cartridge cases were found on the cafe floor, suggesting the number of shots Monis fired.

But Mr Murphy said it was virtually impossible to determine how much use the gun had.

"I really can't estimate whether it's been fired tens of times or hundreds or thousands of times," he said.

It creates further mystery around the history of the gun before it came into the hands of Monis, a matter which appears not to have been determined by police.

The inquest continues.