Okay, so, proposed dice system. This is a very simple, rough version of one that a group I played with used once. 

You have attributes and skills, and you roll 1d20 with your actions. If you roll less than your skill, you succeed(so, the higher your skill, the higher your chance of success). 
I was also going to add in bonuses for your character's [s]cool-headedness(let's call this trait, Stoicism)[/s] (Actually, we'll go the other way and have a penalty for their panic) and their familiarity with a given weapon. 
Let's say Panic goes from 0-3, 0 being someone who is just improbably unflappable. And the stress of a situation multiplies this. 
Weapon familiarity also goes 0-3, 0 being they just picked it up for the first time. 

So let's say they have a handgun skill of 13, and a panic of 2, the camp's perimeter has been breached(call this stress level 2), and they're using a gun they've been training on the past week(familiarity 1). Panic adds four to their roll(panic level of 2, and stress level 2), but weapon familiarity subtracts 1. You roll a nine. Add 3, and that's a twelve. Under your skill, so it's a successful shot. Let's say you rolled 11 instead, adds up to 14, so you miss what you were aiming for(the head, presumably) but it was a near miss, and you could say you got a chest shot instead. 

What are thoughts on this?