The NATO standard as previously was 7.62 mm, now it has been changed (5.56mm). The primary aim being to increase the logistic load of the enemy-'i am not leaving behind a comrade' thing.
But as we have already adapted 7.62 and are also locally producing it so its not going to change in near future as far as i can understand.
The G-3 can be used as:
A standard assault rifle
Sniper rifle (with telescope)
MG (while on bipot)
Anti tank (the Energa grenade) though not used extensively due to commonly sensed reasons.
In my opinion it is bad CQB weapon, especially for room clearance/entry etc etc.
MP5 and SMG Chinese are guud alternatives.
Given a choice i'll go for the MP5 before i enter a room stuffed with terrorists.
Someone pointed out that G-3 has a problem when fired automatically, well even the MP5 gives you some thrust of you are firing long burst with it and ofocurse it is difficult to fire G-3 at Rapid continuously, that's why the bipot is there. Use it properly on MG role.
And yes the fiber glass body is 'hot'