The order for three shotguns, two revolvers, and a rifle had already been invoiced to the athlete when he shot Steenkamp on February 14 last year, testified gun licenser Sean Rens.
"The transaction was cancelled a month post-incident," he said at the start of the third week of trial.
South African law allows non-collectors to possess only four firearms.
Rens said Pistorius "had a great love and enthusiasm" for firearms.
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"He went into what we call 'code red', or combat mode, in other words to draw his gun and go and clear his house," Rens testified today.
Rens met the double-amputee in 2012 through a mutual friend. At the time Pistorius owned a 9 mm pistol and the pair visited a shooting range together around 10 times.
The state has drawn on previous gun incidents to depict the 27-year-old Pistorius as rash and trigger-happy, in support of the charge of premeditated murder.
Licensing examination records showed Pistorius knew the country's gun laws well, the court heard.
He answered correctly that he could only shoot at a person if his life was directly threatened.
Asked if he could fire at burglars stealing a television from his house, Pistorius answered: "No. Life is not in danger," Rens said, reading from an answer sheet.
Pistorius says he shot dead Steenkamp, 29, through a locked toilet door when he mistook her for an intruder.