Coroner Ian Smith was told Mr Dummer wrote to the McDonald family shortly after the accident.
"I cannot begin to imagine the pain and suffering I have caused you," he told the grieving family.
Mr Dummer said at the time he wanted to do "something constructive" to prevent a similar tragedy in future. "I have disposed of my firearms and have no intention of hunting ever again," he wrote.
But he has since changed his view, applying for a new firearms licence three months ago. He understands police opposed this application.
Recalling the day of the accident, Mr Dummer said he and a hunting friend separated when he wanted to stalk a deer.
"I was in dense forest floor undergrowth," he said. "I heard what I thought was the sound of a deer moving through the bush ... I saw what I thought was the red shoulder blade of a deer."
Effectively, he said, he and Mr McDonald were hunting one another. He fired a shot after seeing an object partially obscured by toi toi.
"I heard it fall to the ground," he said. He then approached. "I saw a guy lying down ... I had a look at him and he was dead."
Mr Dummer went to tell his friend he had killed someone. "He didn't believe me - and I had to tell him a few times."
Cindy McDonald fought back tears to pay tribute to her son. Only 29 when he died, he already had a successful business established with his own savings. She said her son and Mr Williams were both careful, intelligent hunters.
"Cam's death has not only devastated his family but has left a huge void in all his friends' lives."
Mrs McDonald said it was astonishing Mr Dummer could apply for a new licence just two years after killing someone - and said people found guilty of manslaughter or gross negligence causing death should face a lifetime ban on owning guns.
The McDonalds also want safety guides posted more prominently in every gun shop and a new offence category created between the charges of manslaughter and of careless use of a firearm. They also say gun licences should be reviewed every five years, instead of 10. Mrs McDonald said authorities should consider whether people convicted of serious offences, including offences related to alcohol abuse, should face stiffer bans on holding gun licences.
"If it prevents another family suffering the distress and the heartbreak we've endured, it will be worth it."
Mrs McDonald believes Mr Dummer should have been banned from holding a firearms licence after he was convicted following a "road rage" incident.
The court was told he was arrested in New Plymouth in late 2011 and convicted of charges including assault with a weapon and intentional damage.
Mr Dummer said he was "upset" the assault conviction was mentioned, and dismissed any relevance.
He blamed the Department of Conservation for not monitoring hunter numbers in areas such as Aorangi Forest Park.
"If too many people are using the area it does become congested and somewhat unsafe," he said. "... In a lot of hunting areas you get a permit and that's the end of it. They don't monitor who's going in or out."
Mr Dummer said Mr McDonald was wearing camouflage clothing other than a "blaze orange" cap.
Coroner Smith asked why all hunters did not wear more bright colours and less camouflage gear - since deer viewed the colour spectrum differently and wearing more bright gear would not reduce chances of a successful hunt. Coroner Smith reserved his finding.
