You guys would've probably liked my machine gun demo, at IndieMeet:
http://www.facebook.com/video/video.php?v=10150260741662323
As for the original question, I agree that it depends on your needs. I find that using a compositing gunshots (using After Effects, etc.) works great. There are excellent gunshot collections, for as little as $20 from
NCCinema,
DetFilmsHD
Action Essentials from
Video Copilot
Just for yuks, if you need a plane blowing up!
http://www.detonationfilms.com/EffectPreviews/747preview.html
There is an aversion on this forum to using real guns, which is well founded - based on stupid filmmakers getting people hurt or killed. It's good that we now have alternatives like blank stage guns or visual effects. However, computer effects weren't available when I started out. We used real guns (with blanks) on films for many years. But, even a blank can kill an actor, like the guy who pressed the barrel against his temple. There was no bullet, but the discharge of a small explosion needs somewhere to go. Putting that thing against his head was like holding a small firecracker and wrapping your fingers around it. Hand open and you get burned. Hand closed and you've made an enclosed casing of flesh; fingers will get blown off.
What I'm saying is that the common sense that we use to deal with the danger of real weapons, must extend to blank firing props and even a plastic replica. The plastic replica won't fire, but actors/filmmakers acting stupid and waving them around in plain sight can scare people. Someone calls the cops and they don't see a red safety tip (because you painted it black), so they don't know that the guns are fake. Worst case scenario: death by cop.
Assuming you have permits and an armourer, a blank firing shotgun blowing papers off a desk may require a real shotgun and a blank.
I recently had a scene in a very dark hallway, so I needed machine gun rounds to light up the place. I went with a blank prop gun.
In almost all other cases, I go with After Effects, because blanks are loud and I don't want unwanted attention. When we made THE AWAKENING, I was all about the blank firing guns. My FX guy, Kelly, preferred CG, even though he was a military guy. One reason was that the non-military actors tended to react apprehensively, when firing a blank. We had a take where a marine captain fired a blank and then without the blank. We ended up using the "pretend" take, because he blinked on the blank take. Ironically, the CGI take looked every bit as real as firing the blank! That really turned my attitude around about using FX.