Common sense. On New Year's Eve, we fire into the ground, or into a tree trunk. The gun isn't going to go 'Bang!' any louder by shooting into the air, as opposed to into a backstop of some sort.
Having said that, the Million Mammary March can still go to hell.
![](http://www.palos118.org/South/curriculum/team6c/midages/vikingss/vikingman.gif)