His immediate shock was compounded when 14 police officers, more than half of whom were armed with semi-automatic rifles and side-arms, left the vehicles and spread out across his front yard.
A dog unit was also present, and backed up two plain-clothes detectives who approached his front door to speak to him.
Mielnik, who manages 6000 cows on a dry-stock farm in Westerfield, about 20km outside Ashburton, said there had been no warning of the raid, which he described as "over the top".
"Fortunately our two young children [5 and 11] were at school at the time, but you can imagine how traumatic it would have been if they'd been playing out front when all these armed police turn up."
The detectives began by explaining the reason for the raid was Mielnik's purchase of an AR-15 semi-automatic rifle from Gun City, the day after the Christchurch terror attacks in March.
After seeking his permission, they conducted an "intrusive" search of his property, then asked him a series of "pointed" questions.
"They were very interested in my views on the Christchurch shooting, Muslims, religion, and politics. I don't hold extreme views. To imagine I'm some sort of white supremacist is just a bit far-fetched."
Following the interrogation, the detectives told Mielnik they would need to confiscate his AR-15, worth about $2600, and $400 of accessories and ammunition.
"I wasn't best pleased to be honest. I'd only bought it on the spur of the moment as I was originally lined up to get one for my birthday for target-shooting, and just thought, 'I'm never going to be able to get one now; better move quick'," he said.
"Then when the ban came in a few days later, I tried to do the right thing and return it to Gun City to get my money back, but they weren't interested."
Mielnik said he understood the reasoning behind the rifle ban and seizure, but not why he was targeted in such a heavy-handed manner.
"I'd like to know how I came to be on a list somewhere. I'm just an everyday Kiwi. A phone call would have worked just as well."
Contacted by the ODT, police said they could not give details about the number of similar raids that had occurred since the March 15 attacks for operational reasons.
Although they would not comment on Mielnik's experience, they said many individuals had been spoken to as a result of inquiries following the attacks, and "interventions" including arrests had ensued in a few instances.
"That is normal policing ... anyone is welcome to make a complaint if they believe police have done something wrong ..."
Mielnik said he did not plan to lodge a complaint, although he and his family had been left unsettled by the incident.
"It doesn't seem right they can treat people like this. It's very worrying."
