Coroner Ian Smith was told 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 Cam's grieving family.
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 Dummer had since changed his view, applying for a new firearms licence three months ago. He understood police opposed this application.
Dummer recalled the day of the accident. He said he and a friend hunting in Aorangi Forest Park 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 shoulderblade 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."
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. She said Cam, only 29 when he died, 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 friend's lives."
Mrs McDonald said it was astonishing Dummer could apply for a new licence just two years after killing someone - and 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 "careless use of a firearm." They also say gun licenses should be reviewed every five tears, instead of the current ten years. 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 said Dummer should have been banned from holding a firearms licence after he was convicted following a "road rage" incident.
The court was told Dummer was arrested in New Plymouth in late 2011 and faced charges including assault with a weapon, and intentional damage, for which he was convicted.
Dummer said he was "upset" the previous assault conviction was mentioned, and dismissed the idea that if his firearms licence was revoked after the assault, Mr McDonald would be alive.
Instead, 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."
Dummer said Mr McDonald was wearing a "blaze orange" cap and camouflage clothing elsewhere.
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.
