Here's a - relatively - easy to replicate strategy for the insanly hard "Mile High Club" hidden mission on Call of Duty 4. This video is done on Veteran difficulty, and took me 8 solid hours to do even once. This strategy easily became the most consistent, and even with just 60seconds to do it in, you can see you can still take time to reload strategically. :) Hope this helps those who truly need it on this devilish achievement.