Norwegian G3 rifles have a thumb size milled portion on the bolt side that can be used to force the bolt home with thumb pressure if it doesn't go into full lock-up when the charging handle is cycled.
I have read where this feature also allows the weapon to be quietly cycled into battery by retracting the charging handle slowly, riding it forward under hand pressure, and then using the thumb to complete the bolt closure.
I have tried this up to the thumb closing portion and, frankly, the rifle cycles so loudly, even under control, that I find this a bit unlikely.
The Norwegian variation is the only G3 that features this bolt closing device in the design.
They were built under Heckler & Koch license at the Kongsberg Vapenfabrik in Norway.