“Converted top-venting blank firing pistols are a popular choice for criminals,” Ms Dummett said.
“They are easier to get hold of than original lethal purpose firearms, but can be used, in just the same way, to threaten, to seriously injure and to kill.”
Mitigating, Hossein Zahir KC said it is “not hard to convert” the guns McKenna made viable.
He said McKenna’s enterprise is “smaller scale and unsophisticated”.
Prosecutors say Razzaq, 44, who was convicted of manslaughter for his role in the fatal raid at family-run Universal Express travel agents in Bradford, West Yorkshire, in November 2005, received firearms for onward sale to criminal customers.
Other customers of McKenna’s converted guns include Allan Crosby, 44, of Etfield Grove, Sidcup, and Ryan Smith, 44, of Morants Court Road, Dunton Green, Kent, who were convicted of possession of firearms and modified ammunitions.
They are being sentenced alongside Tina Smith who admitted four counts and McKenna, who has pleaded guilty to 14 counts.
The charges against the two include collecting terrorist information and possessing a prohibited firearm.
Tina Smith shared McKenna’s mindset, prosecutors say, in one message writing: “Wow they have to be gone from this country, shoot them all.”