[Erasmus]

[...] just enough noise for the actors to all react to the "gunshot," [...]

...such as jumping backward four feet, from the impact.

[GreenLanternCorps]

Only four feet? In the movies a .22 revolver will blow a 300 pound man across a room and through a plate glass window...

http://tvtropes.org/pmwiki/pmwiki.php/Main/BlownAcrossTheRoom