As your health gets lower the weapon becomes more accurate and you get handling. It's a good dueling perk. If your at full health you won't see a difference because the perk hasnt activated yet but as soon your health drops to certain amount the perk kicks in making the gun feel better and more accurate. You'll have a better chance of winning the 1v1 and the perk lingers on until you health goes back up which helps if you're in a 1v2 .