During his earlier evidence, Dr Alexander Dempster used the silencer-equipped Winchester .22 to show how difficult it would have been for the right-handed Robin Bain to shoot himself in the left temple with the rifle that killed the family on June 20, 1994.
But defence counsel Michael Reed QC yesterday showed Dr Dempster a series of photographs prepared by a British ballistics expert the defence would be calling.
The photographs depicted several different positions Robin Bain could have adopted to use the gun on himself.
Dr Dempster agreed they were more likely scenarios than his demonstration to the court on Tuesday, and that it was possible for someone to fire the gun in the various positions where the person was leaning over the gun, with its stock on the floor or resting on a chair and the person with his foot on the chair.
He accepted it was not necessary for the person in the pictures to contort himself, or for the gun to be held in the air, and that it could have been resting against a chair.
The Crown case against 37-year-old David Cullen Bain is that he shot his mother Margaret, sisters Arawa and Laniet and younger brother Stephen before lying in wait for 58-year-old Robin and shooting him from behind the curtains of the computer alcove in the family's Every St home; and then made it appear as if Robin had killed himself.
The defence says Robin committed suicide after shooting his wife and three of his children, his motive for doing so being he was suffering from depression and about to be unmasked for having an incestuous relationship with 18-year-old Laniet.
The trial, before Justice Graham Panckhurst and the jury of seven women and five men, goes into its 23rd day of hearing today.
In response to Mr Reed's questions about the photographs, which, the defence says, illustrate the ease with which the person - with a shorter arm span than Robin Bain's 185cm-180cm - could reach the trigger, Dr Dempster said it was not the easiest way.
He said he was surprised the person was able to reach the trigger with his thumb, as shown in one photograph, but said he accepted it was feasible for a person to shoot himself in another of the positions where the man was standing and leaning forward.
Pressed further by Mr Reed, Dr Dempster agreed it was "quite likely" that if Robin Bain was going to commit suicide, he would have adopted one of the positions shown in the defence photographs rather than the position shown in his demonstration to the court.
Mr Reed then told Dr Dempster the defence would be calling two overseas pathologists, Dr Robert Chapman, who was "famous for doing the autopsy on Princess Diana", and Prof Stephen Cordner, the chief pathologist in Melbourne.
While they agreed with him (Dr Dempster) "in most regards", Dr Chapman would say the site of the wound to Robin Bain's left temple area was not unusual for a suicide; that it was "an elected site", Mr Reed said.
And Prof Cordner would say there was nothing suspicious about the angle of the wound trajectory.
Dr Dempster agreed about one in eight of those right-handed people shooting themselves in the left temple did it in the exact area the bullet had entered Robin Bain's head.
He also agreed it was "perfectly feasible" to have a bullet wound to the head matching the exact degree of travel of the bullet in Robin Bain's head if the gun was applied in the correct way, "but he's chosen an unusual way of applying the rifle to his head if he's chosen to kill himself with a rifle".
He agreed the photographs showed it was possible.
Asked about his theory that it was unlikely Robin Bain would have worn a hat if he shot himself, Dr Dempster accepted he did not know whether the hat would have been on Robin Bain's head or whether it was possible he had pushed it off before shooting himself.
And he agreed test shots at pigskin tended to support his original interpretation that the wound to Robin Bain's head was a contact wound.
Prof Cordner and Dr Chapman both agreed it was a contact wound, neither of them having seen any powder abrasions, Mr Reed told the witness.
But Dr Dempster said the thing that concerned him was the possibility the silencer could interfere with any powder marks.
He agreed he had said at the depositions hearing in 1994 it was a contact or close-contact wound surrounded by an area of soot or powder deposition, and that had been his evidence at the first trial in 1995.
Asked about a red spot on Robin Bain's eyelid, which Prof Cordner would say did not have any of the characteristics of a powder abrasion, Dr Dempster said he could not completely exclude that it was a powder abrasion, but he agreed it was "very unlikely" it would be, and that he had seen no evidence of powder abrasions at the time.
Another issue Mr Reed put to Dr Dempster was that of a live bullet found near the rifle on the floor beside Robin Bain's body.
A UK expert would say it was the result of a misfire before it was ejected, Mr Reed said.
He also suggested it would not be very logical, if the rifle had to be cleared before another bullet could be fired, and the gun was poking through the curtains and almost touching Robin Bain's head, that he (Robin) would have simply stood and waited while the gun was cleared and reloaded.
"It's just plain barmy, isn't it," he asked.
Dr Dempster said he would not use an emotive word like "barmy", but he said it was "unlikely".
The order of the shots fired at Laniet was also covered by Mr Reed.
Dr Dempster earlier said he believed the first shot was the one to Laniet's left cheek, as she would have continued breathing after that and could also have moved to touch the wound, explaining blood on her hands.
She was then shot twice more, through the top of the head and above the left ear, both of those shots being potentially fatal.
The Crown says the fact David Bain talked of hearing "gurgling" from Laniet's room points to him as the killer.
But Mr Reed said tests done in Melbourne on bullet fragments retrieved from Laniet showed there were white fibres on the fragments, both from her head and in the room.
And defence evidence would be the bullet was fired into the top of her head - "an execution type of shot"- as she was partly sitting up, and had passed through an intermediate target, breaking up before hitting the skull.
Dr Dempster said he could not exclude the defence theory that Laniet was shot first in the top of the head and then twice in the side of the head.
And he could not exclude the possibility she continued to breathe for some time after all three shots were fired.
It was a difficult issue, he said.
Public interest in the trial has remained constant and the upstairs gallery was packed throughout most of yesterday's hearing.
And there was a longer morning break after one of the jurors became tearful during some of the graphic evidence about Robin Bain's wound.
