Horse breeder and trainer Greg Meads held a double-barrelled shotgun centimetres from his wife's throat before pulling the trigger, a jury has been told.

The 55-year-old Meads is on trial in the High Court at Hamilton for the murder of his wife 42-year-old mother of three, Helen Meads, at their Matamata home in September last year.

The court has heard that Mrs Meads told her husband that she was going to leave him.

Four days later, he walked into a stable where she was working and shot her.

Dressed smartly in a blue suit, Meads showed no emotion as a jury were shown an image of the fatal gunshot wound to the lower right side of his wife's throat while an expert witness detailed how he must have been in close range to cause it.

ESR forensic firearms examiner Angus Newton said the firearm's muzzle was in "loose contact" or "very near" to Mrs Meads' neck when it was discharged.

"By loose contact I mean the muzzle is loosely touching the skin and not hard pressed up against the skin," said Mr Newton.

"It was approximately no more than five centimetres [from the neck] in this instance."

Another firearms expert, police armourer Robert Ngamoki, said he tested the shotgun by hitting it with a mallet and dropping it to the ground.

He said the weapon was in good condition, and was unlikely to have discharged accidentally.

Meads' lawyer Murray McKechnie is seeking a manslaughter conviction, saying his client had never intended to kill his wife.

Mr McKechnie had earlier argued that Meads did not intend the gun to go off, and "did not take aim at her".

Stablehand Sean Kesner had earlier said things appeared to be normal between the couple despite their impending breakup.

Mrs Meads appeared to be her "usual bubbly self" moments before her death.

On September 23 last year, Mrs Meads was chatting on her mobile phone to a friend in a stable at their home when Greg Meads waited for her to finish talking before shooting her.

Matamata police constable William Hickey told the court how he recovered Mrs Meads' phone shortly after the shooting.

On it was a text message that read: "I am sweet. It may take some time but he's going down. When I'm finished he will be f***** I'm in the best mood. When are you in Rotorua? When are you back ?"

The trial, before Justice Allan, continues today.