Currently when a weapon with a fixed magazine reloads a partially empty magazine, at least when it is able to be single loaded, your character inserts the exact amount that was missing before opening the bolt. So if the mag is 2/5, you put in 3 rounds. This is not how it would work since opening the bolt will always eject the round currently in the chamber (unless you press down on it carefully when opening the bolt which none of the animations actually do). So I suggest the following:
Reload one more round than what is missing, and there should be a full reload if there’s just one round left.
So in the case of 2/5, 4 rounds should be reloaded.
1/5, full reload
4/5, 2 rounds etc.
I’m not asking for the ejected round to be treated as spent however, just that the animations should reflect how these weapons work in reality.