Two things are most important here.
- Make sure nobody gets hurt (a bad example of this being Brandon Lee’s death)
- Don’t break the law (because that might quickly ruin your film project and life)
Apart from that, other factors in the equation are
- How real does it look?
- Are we going to make people call the police?
- How expensive is it?
Blank guns
- Pretty dangerous because blanks contain more powder (and therefore generate more pressure) than real guns. Being too close to one can not only hurt someone’s ears.
- Very loud – not too unlikely someone will call the police if you did not select your filming location well
- Look very real even in close-ups
- Not too cheap if you want nicer models
Softair guns
Blowback – These softair guns behave like the real gun in that they move the slide backwards with each shot, which quite realistic, although you have to add muzzle flash in post production.
Non-Blowback – Typically cheaper their blowback counterparts but you have to plan your shot (camera not gun) so that it is not too obvious, it is not a real gun. You can get away with this quite well and it is done in hollywood blockbusters as well.
Especially if you have scenes with a lot of people carrying (but not necessarily using) guns, I don’t see a better/cheaper option than getting lots of cheap (I buy broken ones whenever I see them) softair guns (even the cheapest ones look good enough from a distance).
Special film guns
They exist, I don’t know much about their legal status but only that they are too expensive for my budgets so I won’t cover them here.
Information about guns
If you want to know which model of a gun was used in a certain movie to get a softair or blank version of it, the Internet Movie Firearms Database is probably worth a look.
lowbudgetactionfilms 