GURPS Is Reality

No, it's just a game.

But I like to see how well it can simulate things.

Like a shotgun at contact range to the chest not being an instant kill.

Let's assume it's a 12ga, 2-3/4" shells and buckshot.

Each of the 9 pellets is capable of doing 1d+1 pi, but p. B409 gives rules for extremely close range damage.

Muzzle in contact is well below the 4 yards which is 10% of 1/2D range of 40.

So we multiply the 1d+1 pi by 1/2 the number of pellets, rounding down.  9 / 2 = 4.5 or 4.

1d+1 x 4 = 5.14 or 5d pi.

The target is wearing a shirt, so no armor to worry about.

The average person is straight 10 stats, so he's got 10 HP.

5d pi will do 5-30 points of raw damage, but he probably hit the vitals with this shot, so x3 to damage giving us 15-90 points of damage.

The average, honest, six sider gives 3.5 points per roll.  Five of them average to 17.5 or 52.5 to the vitals.

You have to make a conscious roll when you reach 0 HP and every second after.  You have to make a death roll every time you cross a negative multiple of your HP, -10, -20, -30, -40 in this case.  You are automatically dead if you hit -5xHP, or -50 in this case.

If you fail a death roll by 1 or 2, you're mortally wounded rather than dead.  If you make your consciousness roll(s), you're still incapacitated, but awake.

You check for bleeding at HT-(damage taken/5) every minute after being wounded, critical success means you stop bleeding, success means you take no additional damage, failure means you take 1 hit and a critical failure means you take 3 hits.

Minimum damage isn't even lethal!  -5 HP does even warrant a death roll

Average damage, though, certainly is.  -42 points is 4 death rolls and a consciousness roll.

If you make those rolls!  You're not moving very fast, and you're bleeding.  You roll against your HT-(damage taken/5) to prevent losing an additional HP per minute (HT-10 in this case or 0 or less to succeed).  -42 is a mere 8 points from auto-death as well.  It gets better!  You lose 3 HP on a critical failure, a chance of zero means any roll of 10 or higher is a critical failure.  The average roll of 3d6 is 10...  So three minutes of bleeding, maybe four, should do it.
Three minutes is 180 turns of activity!  Our guy is clearly more hurt than this, but not much more as we'll see.

Maximum damage knocks him down to -80 HP, or well past the -50 HP required for auto-death.  Any raw roll of 20 or higher is automatic death, in fact.

I think our assailant rolled a 19 for damage, doing 57 points to the vitals dropping him to -47 HP.  He made his consciousness and all four death rolls for the turn he shot himself, and kept making the consciousness rolls until he moved off screen where he finally passed out and then made a critical failure on his bleeding check for three more HP to hit the automatic death point of -50 HP.