For the young, inexperienced and and non-mil types on here,
The term 'gun' is usually used on things over 20mm. Hence a gun is used by the artillery (105mm, 155mm), etc.
However, the generic term 'machine gun' is usually referred to something belt fed. MGs here are called GSMGs, GPMGs, and LSWs. I rarely hear the word 'machine gun'.
In civvy world a 'gun' is a 'rifle' ( a clip is a mag), but in the world of the military we all know that these guns are indeed rifles or carbines. They can also be called personal weapons, plus they can be called what their nomenclature is, say C7, C8 or F88, F88C, etc.
If you were to call a rifle a gun here, you'd be getting a chewing from the nearest NCO quicksmart.
Cheers,
Wes