For me the 2nd nuke is the hardest, so much random crap happens. The first was the easiest, I didn't camp, run and gun, knife, or tube. I used a fiddy cow on wasteland domination, and made my way around the map killing people as I go.
For my second nuke, I was on 24 kills, and some [censored] with a thermal sniper killed me, with the magic bullet effect, and I was just about to line a guy up

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EDIT: Some other scenarios include, being killed whilst in my chopper gunner, getting my chopper gunner shot down almost through and getting insta killed, going to 23 kills with an intervention (wasn't even using chopper gunner) and the game ending, killing myself with a chopper gunner and just plain dying before the 7 kill streak.