Just a humorous conversation I had on FB on how possible it would be for David to kill Goliath so quickly in D&D terms. Some earlier, less insightful posts, are not included.

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  Me: David kills Goliath with a sword, not a sling. David hits him with a sling (since Goliath is aware of him, the only way he's getting sneak attack damage is if Goliath lost initiative and is flat-footed when David looses -- David might need a certain feat for that), gets a stun and knocks Goliath prone. Then, while he's stunned, Dave picks up Goliath's sword (short sword for Goliath cause that's all they had in the Bronze Age, translates to I guess a broadsword in Dave's hands -- as a rogue, he may still be proficient depending on which edition of D&D we're playing) and attacks stunned, prone Goliath, gets sneak attack damage if G money is denied his dodge bonus for being stunned.

  
  
• Me:  With the right feats, Dave might have gotten sneak attack damage with the sling, and more sneak attack damage with the sword.

  
  
• MD: Surely the sword was just the coup de grace?

  Me: I don't think being prone and stunned leaves you vulnerable to coup de gras. If the sling knocked him unconscious, maybe. Let me check my Bible. 

  Me: and/or Players Handbook.
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  MD: "David ran and stood over him. He took hold of the Philistine’s sword and drew it from the sheath. After he killed him, he cut off his head with the sword"
  
  It's a little vague whether or not the killing happens with the sword, or if it's poetic, and the sling did it.
  
  That said, without a weird build, I don't know of any way for a sling to make one both prone and stunned without just knocking you out. Stunned alone would leave Goliath upright.
• Me: Which leaves Liz's objection: How are you going to reduce a giant to 0hp with a slingstone, critical hit or no? Even if David is a 20th level rogue and Goliath is the smallest kind of giant, it's a tough damage roll.

  
  
•  David IS a rogue, because his brother tells him" I know thy pride, and the naughtiness of thine heart" 1 Sam 17:28

  
  
•  Tough, but not impossible. Especially with assorted divine favors/GM fiat. Though Goliath is only said to be 9 feet tall and change, so maybe he was a troll. Or a human with Enlarge Person made permanent on him.

  
  
• Me: He isn't 20th level, because he is but a youth (1 Sam 17:33) and the most impressive beasts he has killed before Goliath are a lion and a bear (1 Sam 17:36)

  
  
•  Troll would have regenerated even after losing his head.

  
  
• Me:  Human with Enlarge could work.

  
  
•  We know David does not have any level of fighter or paladin, because he is not proficient with swords or armor (1 Sam 17:39)

  
  
• MD:  At what point do diminishing returns on wolves kick in for XP? A Lion and Bear are impressive, but if we assume that he's killed a crapload of wolves as a shepherd, he's only good for what, level 5?

  
  
• Me:  In 3.X D&D, wolves and even lions would be worth 0xp well before level 10.

  
  
• Me:  If we presume that Saul has levels of cleric, Saul may be placing a buffing effect on David in 1 Sam 17:37.
• MD:  Yeah, even one bear is probably of marginal help.
  
  That said, we're not looking at much for Goliath either. He's got a follower (shield bearer) and some heavy, presumably masterwork gear, but nothing enchanted that they talk about.

  
  
• Me:  and they never refer to Goliath as a giant. Which means we have no reason to think he has hill giant hit dice. He was a large, perhaps Enlarged human.

  MD:
• Looking at the encounter calculator, David would max out at level 9. And that assumes that by that time, he's killing off wolves in job lots of 20 at a time.
  
  (Level 12 if we assume that he's doing the same thing to bears, but that is pushing the text quite a bit.))
• Me:

   Goliath is a man (1 Sam 17:24), so presumably a human. He could have fairly few hit points.

  Me:
• Goliath has been a fighter since 1st level (1 Sam 17:33) so he got 10hp + Con bonus, but we have no way of knowing how many more levels Goliath achieved.

  
  

  MD: And note, David does not say that he cannot USE armor. Just that he is not used to them. If he took the Vow of Poverty that limits you from using most weapons and wearing armor, he'd get a good handful of abilities from that. (though that may prevent him from using Goliath's sword.)
  
  Basically, if David is a 9th level rogue, and Goliath is a 6th level fighter (minimum for Leadership) stuck with masterwork gear, we're looking at the inspiring story of a PC who kicks the shit out of a character fairly weaker than he is.

  MD: Indeed, David is "Glowing with health" like the ability to resist the elements, manage with the relatively crappy diet of a shepherd, and maybe literally just glowing, all stuff from VoP, or other Exalted feats (including the one that gives you d8 sneak attack die.
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• Me: But David does not have Vow of Poverty (1 Sam 30:20) (2 Sam 6:11) (2 Sam 6: 13) (2 Sam 8:7) (2 Sam 12:30).
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• MD:That's fair. He could have ditched the vow later, but probably not. BoED is pretty cheesy anyways.