Honestly, I didn't think Little Rocket Man was that hard.
Had more trouble achieving Get Some Grub, which just takes huge amounts of patience and stress when you find out you only have 332/333
or the one where you are not allowed to let any buildings be destroyed by striders.
Hardest achievement for me was the "kill a combine soldier with his own grenade"
The one free bullet is actually quite fun to play, I have tried that and I will definately try that again one day.