Come to think of it, pretty much all reloading systems are rather unrealistic, too.
Example:
You have a 10 round clip, and 90 extra ammo.
You reload while you only have half of your clip left.
The extra bullets get back into your... backpack, I guess, creating an incomplete clip.
Given, you do seemingly pull the new clip out of nowhere, but with the reload times in their current state, you wouldn't have enough time to put the half-empty clip back into your... nowhere... and get a new one out (Espescially considering the fact that it'd take a second or two longer, due to the fact that you always grab the half-empty clip last, so you'd need to organize them in such a way as to grab that specific clip last.)
Example 2:
Let's say your reload time does account for putting the half-empty clip in your bag.
So, you're fighting, and there is a half-empty clip in your bag. (10 round example clip still.) You have pushed your enemies back, giving you a few seconds to reload. There are currently 2 bullets left in your clip.
Somehow, those 2 bullets combine with the half-empty one, to make a clip of 7 bullets.
If you were really fighting, I doubt you'd have the time to take both clips out of your bag and transfer the 2 bullets to the half-empty clip.
However, considering this is a game, let's say you DID have the time to transfer those 2 bullets.
That's not really been implemented in these weapons. (Or really ever, (To my knowledge.) as it'd be a bit complicated, due to the amount of remembering numbers you'd need your script to do, (i.e. if you have 2, half-full clips, and don't combine them, you'd need your script to know to go through the process of giving you a partially empty clip twice.)) Unless you did take the extra 3 hours or so to script this out, the only way to get around both of these problems would be to have the player drop the clip.
Please note, I don't intend for you to implement this.
I'm just stating, that if you want the extra ammo things to be realistic, you should probably make the reloading system realistic, but, to do that, would be, as demonstrated above, extremely complicated.
Actually, the gist of what I meant to say, would be "Real Life is loving complicated."