Yeah it says that the magazine is emptied. So if you have 1 round left, RAW, you can technically roll 1 ammo die hoping for that extra 6.
If you have 6 rounds, you can roll up to 6 ammo dice (depending on your ROF), but you'll only get 1 extra success even if you roll multiple 6's. You'll just remove extra rolled 6's from that pool. All other numbers stay. Ovbiously this is super risky and you have an equal chance to roll mishaps.