Saimen,
Merry Christmas,
As Tom has suggested, focusing your question could help in analyzing your problem. Several helpful questions could include:
1. What do you want to survive?
2. How would you happen to encounter that situation?
3. What needs would you want the gun to fulfill?
Incidentally, do read the earlier thread that someone (Hawk?) suggested. A similar topic to yours was discussed a couple of months ago. Moreover, the basic theme of survival guns has been discussed a number of times on this forum, especially over the past year. You may find a search of the relevant topics to help clarify the matter for you.
Best wishes,
John