I always disliked the magazine system because whenever I would reload, I would lose the bullets in the old magazine. ( I prefer to keep my weapon fully loaded as often as possible) The system is fine with me if the old magazine is not discarded, but kept for later use. (Like the system used in SOCOM 1-3)
Yeah Battlefield uses the mag system and I can't stand it, especially when I'm sniping because if I take like two shots and then run off somewhere, I like to reload without losing a whole magazine's worth of ammo.
It'd be nice to stash unfinished clips back onto your belt to use last, or to replenish in your downtime. It'd be a pretty dumb soldier to just cast away a magazine with 1 cartridge missing.
in fact we would more likely go on the "keep you're old magazine" system and "fusion two partial magazines" that way you can convert atwo half loaded magazines into one fully loaded one, thanks to that you'll never be losing bolts all the time, but to "fusion" two magazines you'll need time so you will have to do it away from the battfield or you're dead
Personally, I'd prefer the magazine system. Although I am guilty of reloading every five seconds as to stay topped up, I think it'd be a good addition. As others have mentioned, keeping your half empty magazines as opposed to simply losing them. As for combining magazines when you have some downtime; correct me if I'm wrong, but isn't there a whole thing about each round being blessed and covered in holy unguents etc. before being loaded into the magazine - especially for bolters. I vaguely remember reading something about that in the Deathwatch RPG book.
I'm not sure how the Eldar are handled in the TT, but in other media there weapons still have finite ammunition which can be handled in some fashion, as for why the Orks don't do it, seems like it would be grot work and not something they'd bother with when they could be stomping their way to the next fight.