Robert Barnes' evidence proved damning of Eastman over the 1989 murder of the ACT's police chief, linking him with what the expert said was PMC brand ammunition particles, found in the accused's Mazda and at the scene of the murder of Assistant Federal Police Commissioner Colin Stanley Winchester.

But the current Eastman inquiry is slowly picking over Mr Barnes' work, raising a series of questions about its veracity and reliability.

Mr Barnes gave evidence about a "significant characteristic" of PMC ammo, something he described as its tendency to keep its round shape after firing.

He used that to exclude other ammunition, including Winchester brand, from the particles found in the Mazda and at the scene.

At Eastman's trial, a photo of the particles was handed to the jury which Mr Barnes used to show its tendency to keep its shape after firing.

But Mr Barnes' colleague at his Victorian forensic lab, Professor Norbert Strobel, had produced a similar photo of PMC particles as part of a thesis he was working on.

The two photos were shown side-by-side to Mr Barnes on Wednesday, before the expert was questioned by inquiry head Acting Justice Brian Martin.

"Seriously Mr Barnes, the one at trial does not show any particle that has lost its shape, does it?" he asked.

"It's vastly different, isn't it, from the particles in [Professor Strobel's] thesis?"

The judge then asked whether the jury would recognise the difference between the two photos.

"When I look at the photo on the left, it looks pristine," Acting Justice Martin said.

"Did you select that deliberately because it supported your argument?"

Mr Barnes denied that he selected the pictured to help "bolster" his evidence.

The expert did not prepare a single report in the six years between 1989 and 1995 setting out the tests, observations, and findings upon which he based his assertion that PMC ammunition kept its shape.

Counsel Assisting Liesl Chapman, SC, questioned Mr Barnes over why no reports had been made.

Mr Barnes said he only completed reports on request, and the AFP had never asked him.

"Is that your best answer to why, in six years, you didn't produce a report?" Ms Chapman asked.

Mr Barnes said:

"I produce reports as requested by the AFP, I wasn't asked for one, so I didn't prepare it."

The expert said he discussed the issue with PMC ammunition with his colleague, Professor Strobel, and he had agreed that it kept its shape after firing.

Professor Strobel has already given evidence to the inquiry that he never discussed the issue with Mr Barnes.

The inquiry continues on Wednesday afternoon.