The laws surrounding space can be pretty vague. They are almost similar to laws surrounding the internet, but the main difference is in cases where we do not have new laws to deal with the internet, we have old ones to fall back on, such as copyright laws. Space law only happened 60 years ago, and nothing else really applies in space. It is important to note the time frame and setting in which these laws were conceived. It started in 1957, with the first treaty being created in 1967, and the most recent one in 1979. Laws regarding ownership of objects in space and the use of weapons in space are all based around the Cold War.
There is some debate over what the laws actually mean. Ownership laws, for example, basically state that everything in space belongs to everybody on Earth. In 1967, that probably meant that no country could claim ownership of the moon. While this is not a bad idea, it doesn't really deal with the more modern possibility of a company deciding they want to mine an asteroid. Some space lawyers - yes, they exist - have argued that the broad definition of the law should also mean that asteroid mining and similar activities are illegal.
If in 20-30 years Google decided that it wanted to use some of their ad shekels to mine some rare space elements, would they be held accountable by international law as nations are under the space treaties, or would it be a domestic issue? In the US, there is a law that gives a framework for conditions under which companies can become subjects of international law, but that law came into effect in 1949, and really does not apply to this possibility.
With more and more private companies starting to invest in space, and seemingly less and less interest from countries, we could be dealing with this issue fairly soon.
Edit: I also forgot to mention that conventional weapons are legal in space. Laws regarding weapons in space only involve nuclear weapons. Companies could send security up into space with guns. If they shot someone, it would probably be legal, because there is no law that prevents it from happening in space.
Even if you don't get blown off, you're getting blown backwards. Something like 50% of the force is turned into heat energy and sound and all that with firing, but you're absorbing most of the other half. If I'm not affected by any gravitational forces and fire a gun straight ahead, I'll now be going backwards somewhere around 60 m/s if I'm firing that old musket (which I couldn't). Modern guns would be closer to 90 m/s. It's a force humans can withstand safely, but you're going to be moving away from your target extremely quickly; if something happened where you shot at an odd angle or something, you might even be traveling in an oblique line to your target rather than a straight line away; or else maybe could even be rotating somehow.
EDIT: And I'm not familiar if a gun was ever shot in space or not.