Standard riflemen aren't supposed to be snipers. Obviously, compared to an SMG and whatnot they are far more accurate, but the Mosin Nagant of the 40s is the AK of today.
If you are about to enter a room with a bolt action rifle (which they did all the time), then it would be common sense to top off the rifle.
Just like soldiers change magazines when they are about to enter a new room/area with an AK, M4 ect.
You never want to be caught in a situation where you are under fire and out of ammo.
It would take a while to do so, but it is better than nothing. Because it takes a long time, I doubt it would be used a lot. Especially since this means you will eventually be reloading from half clips, which will take a long time.