An RCMP expert in firearms says the gun the Crown alleges was used during a fatal armed robbery went off on impact during testing at a laboratory in Ottawa.

Laura Knowles was the first witness as Week 3 of the Brandon Phillips first-degree murder trial began Monday.

She examined the Winchester 12-gauge pump-action shotgun model 2200, which was shortened on both ends, as well as a shotgun shell, pellets and a wad.

Laura Knowles, who works at the RCMP's crime lab in Ottawa, testifies Monday at the Brandon Phillips murder trial. (Fred Hutton/CBC)

During testing, Knowles dropped the shotgun six different ways from a height of two feet, the jury was told.

If I hit the top of the receiver with the mallet with moderate force the firearm would discharge. - Laura Knowles

When the gun was dropped upside down, it discharged automatically, she testified.

Using a rubber mallet, she then hit the shotgun multiple times to see when it was susceptible to discharge, she explained.

"If I hit the top of the receiver with the mallet with moderate force the firearm would discharge," Knowles testified, adding it was tested with the safety off.

"The shot would be fired on impact. There wouldn't be a lag between impact and the shot fired."

She then tested other unmodified Winchester models and the same thing happened — it discharged when it was struck with moderate force on the top.

"You can't reproduce every person's grip and you can't reproduce every person's force," Knowles said, but added the gun was held in a plastic device to mimic the way a shooter would hold the gun as she tested it.

Brandon Phillips, 29, seen at the start of Week 3 of his first-degree murder trial at Newfoundland and Labrador Supreme Court in St. John's. (Ariana Kelland/CBC)

She examined the inside of the gun and found that nothing was altered or out of the ordinary.

Knowles told the jury she suspects there is an issue with the spring on this model of gun.

She was so intrigued, Knowles said, she looked for recalls on the guns and contacted the manufacturer to ask if it had received similar complaints.

Knowles never received a response.

She also examined three pieces of wood that were discovered at the Captain's Quarters Hotel after Larry Wellman, 63, was shot by an armed robber.

Knowles said she determined the three pieces fit together and were likely part of the gun seized by police from a home on Quidi Vidi Road.

Defence focus on Wellman's use of table

In past weeks, the defence has focused on contact shooting victim Larry Wellman had with the gun held by the armed robber.

Mark Gruchy asked bar patron and witness Shawn Deeley repeatedly if he saw Wellman use a small table to strike the robber's gun.

Video of the armed robbery and shooting, which was taped at one frame per second, shows Wellman use a small table to thrust at the shooter before he drops to the ground.

During cross-examination, Gruchy pointed out that "moderate force" could mean different things for different people, given their size.

"Even a high level of force of severe level of force would produce the same effect," Gruchy put to Knowles.

"Yes," she said.

Three pieces of wood were discovered at the Captain's Quarters Hotel in St. John's after a fatal shooting on Oct. 3, 2015. Firearm expert Laura Knowles said it's possible the wood was part of a Winchester shotgun. (RNC photograph )

Crown prosecutors Mark Heerema and Shauna McDonald will likely wrap their case this week, with the defence presenting its case as early as Friday.

It's expected Tuesday will include testimony by a DNA expert and crime scene analysts will take the stand on Wednesday.

Janet Hutchings, the bartender who was working the night Wellman was shot, will be called to testify Thursday.

There is no word on when Premier Dwight Ball will testify at the first-degree murder trial.

He confirmed last week that he had received notice he may be called as a witness.

At the time of the alleged murder, Ball's daughter, Jade, and Phillips were in a relationship. They are no longer together.

Follow the latest from the trial on our live blog.

So far in the trial, the jury has: