I did some scouting around the net about all purpose bush/pack guns, so here's some rescources for you.

Rifle cartridge lethality
http://www.chuckhawks.com/rifle_killing_power_list.htm

Gunfire noise levels
http://www.freehearingtest.com/hia_gunfirenoise.shtml
Keep in mind that decibels is logrithmic, so 10dbl increase = 10X increase in sound pressure and 20dbl = 100X increase in sound pressure. OSHA puts the limit at 140 db for impulse sounds.

Exhaustive threads on an "all purpose" gun.
http://bushcraftusa.com/forum/showthread.php?t=167
http://www.bushcraftusa.com/forum/showthread.php?t=4666

Have fun and know what's behind your target.
_________________________
Hope for the best and prepare for the worst.

The object in life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane