Some comments on the rationale for this... The T5 table was, as I mentioned, is kind of messed up with higher hit probabilities for Right Arm/Leg (11.1%) than Left Arm/Leg (8.3%). Also, the highest hit probability in T5 is Torso at 44.4% and the lowest is Head or Graze at 8.3%. Total probability in T5 is the same for an Arm or a Leg hit at 19.4% It obviously didn't make sense that right arm/leg should be any easier to hit than the left. It does kind of make sense that Torso should be higher than the rest, but 44.4% seemed a little too high. My constraints on rebalancing the table were: 1. Left/Right Arm should be the same probability 2. Left/Right Leg should be the same probability 3. Probability of a Leg hit (left or right) should be higher than the probability of an Arm hit (left or right). 4. Greatest probability should be Torso. That leaves you with only a few ways of re-arranging the numbers for the other hit locations. I opted for putting Torso at 33.3% which was, per constraint 4, higher than any other location, but more reasonable than the T5 44.4%. That basically left me with only two other numbers, 16.7% and 11.1% for either Head or Graze. I opted, kind of arbitrarily, for putting Graze at 16.7% and Head at 11.1%, figuring we'd just see how it worked. I think the possibility of a hit with no damage adds a little something to the game, but I could be convinced to swap these probabilities.

I think they would work, but, as you mention, unless they were bracing themselves, the shooter would be propelled in the opposite direction as the bullet (Newton's third law). This would be true for any projectile weapon like a regular pistol or rifle, a Gauss rifle, or even a bow and arrow. Also, the trajectory of the projectile would be a straight line, not an arc. As I'm sure you're aware (I had to look it up), gunpowder has its own oxidizer (potassium nitrate), so lack of oxygen wouldn't prevent it from working with no atmosphere.