Amendment G-4 would require the firearm to be either a rifle or a shotgun. That excludes handguns, for example. It would have to have a semi-automatic action. It would have to be chambered for a centre-fire calibre, so rimfires would be excluded. It would have to be designed to accept a detachable magazine, which would exclude firearms with fixed magazines, for example. The magazine that it is designed to accept would have to have a capacity of more than five cartridges. Again, that would exclude those firearms that have a detachable magazine that contains five shots or less.
The last criterion is that, when assessing the kind of magazine, it must be a magazine of a type that the firearm was originally designed to accept.