Hypothetical question: when can one use a firearm for defense if they are not licensed?

Just thinking through some hypothetical questions and I honestly don't know the answer for this one. It could apply to someone transporting a weapon legally in their own state, or traveling with a legally stored weapon through a state that does not reciprocate.So you've got your handgun in the trunk, unloaded and stored in the typical legal to transport fashion. Then let's say some scenario arises where your life could be in danger... let's say you're filling up at a gas station and you hear shooting inside. How does the law look upon you should you decide to arm yourself? Let's take it a step further... shooting erupts inside the convenience store, then the armed assailant flees towards your vehicle, demanding your car keys with a gun in his hand and you shoot him. What does the law say about this scenario?I'm not really looking to get into whether or not this is a good shooting scenario, it was just a scenario I tried to paint to illustrate the real question... For those without a carry permit in whichever state they happen to be in - are they allowed to defend themselves should they need to? I would hope the answer is yes, but I'm not sure what the law actually states around cases like this.Thanks for any insight! via /r/CCW http://ift.tt/2FNyBe6