I liked Carlo Hathcock One Shot One Kill.
How long will you last once the bad guys pin you down?
If thats for the 20/30 question, then it depends on the bad guys abilities.
Hopefully we are so far in the bush that there wont' be any shooting or fighting going on there anyway...
But recall, I said I like 20s more than 30s, and thats the prone position issue, I never said I only owned one 20.....