Ok this is a tough quest
Kill 1%
Headshot 2%
Multikills double down triple down etc give bonus
Kill streaks get bonus
Death -2%
If you just get straight kills at around 2.0kd it's possible to go backwards
[spoiler]just do sparrow racing with the last word equipped I got it upto 73% in about 30mins[/spoiler]
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Or, sparrow race with TLW equipped. First place is 3%(ish). Cause someone to crash (I know, bad sportsmanship. Did it once on accident and felt so bad I let him beat me.) gets you a kill 1% No syress, no worries, and kinda fun. Bit of a grind, but so much less stress inducing.