An international ballistics expert has contradicted key evidence that a silencer was used in the 1989 murder of the ACT's police chief.

Suppression orders on new ballistics evidence at the inquiry into the murder conviction of David Harold Eastman have been lifted, despite lawyers for the original forensic investigator Robert Collins Barnes trying to have evidence against their client left out of the inquiry.

The inquiry is reviewing Eastman's conviction for the shooting murder of Australian Federal Police assistant commissioner Colin Winchester.

Last week lawyers for Mr Barnes lodged an application claiming evidence from Irish ballistics expert James Wallace went further than necessary and may harm their client's reputation.

Mr Barnes gave evidence at Eastman's original trial that a silencer had most likely been fitted to the murder weapon.

But on Monday suppression orders on the new ballistics evidence were lifted.

Transcripts reveal Dr Wallace has contradicted Mr Barnes reports saying the evidence shows no silencer was used, and the weapon was most likely a sawn-off gun.

"If you assumed that a person between 120 and 140 metres away heard what he recognised as two shots, but at that distance, if the projectile had not become supersonic, does that suggest to you that there is unlikely to have been the use of a silencer?" asked Eastman's lawyer Mark Griffin.

"It would be extremely unlikely, yes," Dr Wallace said.

"If a person in the next house to the driveway of Mr Winchester's car heard two sounds... like the sound of stones or pebbles being thrown on the roof or against the windows, would hearing such sounds inside a house within 20 to 30 metres of the shots be consistent or inconsistent with the use of a silencer?" asked Mr Griffin.

"It would be inconsistent," Dr Wallace said.

Mr Griffin then asked Dr Wallace "Is it your view that the number of particles recovered from inside the car is more likely to have resulted from the use of a shortened rifle barrel than the use of a normal length... rifle barrel?"

"Yes, I cannot be 100 per cent certain of this but, yes, that would be my theory," Dr Wallace said.

On Monday Dr Wallace was cross examined in court from Mr Barnes lawyer Ian Freckleton.

The questioning has related to evidence given to an earlier case in 2007.

Mr Freckleton repeatedly accused Dr Wallace of raising issues outside his brief, including comments on the eye witness account.

Mr Freckleton accused him of using emotive and strong language to describe Mr Barnes evidence.

"It's indicative of the fact you have abandoned neutrality and adopted the role of an advocate for Eastman," he said.

Dr Wallace has denied the allegation.

The inquiry is continuing.