If the sporting firearm , or A Cat, was fitted with a high capacity magazine it meant the weapon was illegally converted to "E Cat Military Style Semi-Automatics", Mr Plas said.
The owner could be charged with illegal possession, he said.
"Firearms owners are urged to avoid any confusion by ensuring their A Cat guns have none of the features listed (below) and that they have no such items in their possession which may fit their particular A category guns."
An A Cat gun can be classed as a semi-automatic if it has any of the following features:
* a folding or telescopic butt;
* a magazine that is capable of holding, or that, by its appearance, indicates that it is capable of holding, (i) in the case of a magazine designed to hold .22 inch rimfire cartridges, more than 15 cartridges; or (ii) in any other case, more than seven cartridges;
* bayonet lugs;
* a military pattern free-standing pistol grip; or
* a flash suppressor.