The Joy of Guns – Part 1

There have been many different attempts to bring guns into the world of Dungeons and Dragons with varying degrees of success.  How do we drop them into the mechanics of Fourth Edition?

From a modestly scientific perspective I’m going to create some general guidelines for bringing firearms into your game.  We will start with a contest between bullets and armor.

"I never should have charged that AK-47."

This is going to delve into a bit of theory so if that isn’t your cup of tea, you can use the link below to skip to the article’s exciting conclusion.  If you’re ready to “get your geek on” and crank through some science, keep reading.

When is a bullet unlike a crossbow bolt?

Crossbow by Leonardo da Vinci

The heavy crossbow is a powerful weapon that can punch bolts through a steel breastplate.  The 4E rules already account for this with the Armor Class mechanic.  Lighter armors resist the piercing bolts less and your character is more likely to be struck as a result.  At least in this regard, bullets and crossbows should work the same.  A flintlock pistol may not pierce the breastplate unless it is loaded with a large amount of gunpowder.  In this case the normal rules for Armor Class should still apply.

The Flintlock Pistol

The Armor Class mechanic isn’t always the best answer because some high-velocity bullets would simply punch through the steel plate.  High powered rifles will shred steel armor like cheese-cloth and the extra weight could actually be a disadvantage that would make you an easy target.    In this case we would be better suited by letting our more powerful firearms attack the Reflex defense instead.

The d20 Modern system created two new damage types for modern weapons:  Ballistic and Concussive.  I’m going to use Thunder as a handy replacement for Concussive.  Instead of creating a new type of damage, I’ll add a new weapon group for firearms called Ballistic and we will use that and other weapon properties later when we need additional mechanics for things like Kevlar vests.  (I’m avoiding the term “firearm” intentionally because I might want to add futuristic projectile weapons like railguns later to the same category.)

Enter Dr. James Wilson, M.D.

In 1977 at a conference Dr. Wilson presented a paper on bullet wounds which classifies ballistics trauma.

Link: Dr. James Wilson’s Paper on Ballistics Trauma

Citing two key points in his paper:

External Ballistics

“As the bullet leaves the barrel, two very important measurable factors come, into play: muzzle velocity (or the speed of exit of the bullet) and muzzle energy (determined by the mass and the velocity of the bullet). These measurements, together with the flight characteristics of the bullet, are dealt with in the science of external ballistics.”

Bullet Velocity

“Now we come to the most important part of the kinetic energy equation-velocity. Bullet velocity is probably best classified as low (if less than 1,000 ft per second), medium (if in the 1,000 to 2,000 range) and high (if the velocity is greater than 2,000 ft per second). The muzzle velocity of a given weapon is determined by the weight of the bullet and the powder charge, while impact velocity will be determined, of course, by these factors together with the range or distance of the target from the weapon.

Low velocity wounds do little damage other than in the direct pathway of the bullet, for only a small temporary cavity is formed. In fact, as was noted by MacLeod in 1862, blood vessels can actually be pushed aside by low velocity missiles.

Medium and high velocity wounds may be grouped together for purposes of this discussion.  Medium velocity bullets such as the .357 magnum and the .44 magnum create larger temporary cavities and a greater blast effect than do the low velocity bullets like the .22 or .38-but not nearly to the extent as that seen with high velocity weapons such as the M16 or the .30-06.”

Categorizing Firearms by Trauma

Dr. Wilson’s analysis provides the gamer with a ready method for categorizing the wounds generated by different firearms and we can easily use his system to sort our firearms into categories based on muzzle velocity like this:

Wilson’s Muzzle Velocity Categories

  • Low Velocity Firearms: Less than 1000 feet per second
  • Medium Velocity Firearms: 1000-2000 feet per second
  • High Velocity Firearms: More than 2000 feet per second

I’m going to use experimental data recorded by Dr. Stephen Wardlaw with his homemade flintlock:

  • 93 grain ball
  • 600 – 1200 feet per second muzzle velocity
  • 280 foot-pound muzzle energy

Link: Dr. Wardlaw’s Flintlock Article

If the flintlock pistol will occasionally pierce a breastplate and it can be fired at 600-1000 feet per second, it falls into Wilson’s Low or Medium categories depending on the amount of gun powder used.

Guns on the Battlefield

Using Muzzle Energy to Determine Trauma

Next, we can use the muzzle energy to create better categories for determining wounds based on Wilson’s categories and with an eye towards our D&D mechanics.  We calculate the kinetic energy at the muzzle of the weapon using the mass of the bullet and the muzzle velocity.

Kinetic Energy Equation

With regards to guns, most D&D combat is close range so I’m intentionally using the energy when the bullet leaves the muzzle to build my categories.  (If you wanted to play at much longer ranges, you might want to consider the bullet’s energy at different distances.  These are very different when considering handguns versus long guns like rifles and muskets.)

I want the flintlock pistol in the low-powered category so I’m going to use its muzzle velocity (280 foot pounds) to determine my low-end benchmark and I’ll pad it a bit to provide the guys in armor a bit of wiggle room.  (We don’t want to nerf them arbitrarily.)

Dr. Edward Klatt has an article with muzzle energies listed for different bullets which I’m using to tweak my categories.  This sorting is subjective estimation on my part but I personally want Dirty Harry’s Smith & Wesson Model 29 (.44 magnum at 1036 foot pounds) in the highest category so that provides me my upper guideline.

Link: Dr. Klatt’s Ballistics Data

Muzzle Energy Categories

  • Low Energy Firearms: Less than 500 foot pounds
  • Medium Energy Firearms: 500-1000 foot pounds
  • High Energy Firearms: More than 1000 foot pounds

I’m going to rename these as Low-Powered, Mid-Powered, and High-Powered ballistics weapons and I’m going to provide them each with unique attributes.

The Exciting Conclusion

The d20 Modern firearms generally use two damage dice which provides a starting point that I will tweak upwards as we get to higher muzzle energies.  Later, we will give the DM guidance for level-appropriate weapons just as we would with magic items.  Providing this sort of guideline means we don’t have to compromise the weapon’s damage capacity.  Just as a DM can choose which magic items to allow by level, our high-powered ballistics weapons can be guided by the same type of scaling.

Here then are the categories…

Low-Powered Ballistic Weapons


These are early firearms like Flintlocks and low energy modern hand guns like the .38 police special.  One shot from this weapon drops a minion but other monsters may keep going.

Key characteristics:

  • Weapon Type: Ranged
  • Weapon Group: Ballistic
  • 2 damage dice
  • Property: High Critical

Mid-Powered Ballistic Weapons


This includes high-powered handguns, possibly early long guns like muskets, and low powered rifles.  These should ignore armor and do more damage.

Key characteristics:

  • Weapon Type: Ranged
  • Weapon Group: Ballistic
  • Attack: DEX vs. Reflex
  • 3 damage dice
  • Property: High Critical

High-Powered Ballistic Weapons


Our final category includes very powerful handguns, rifles, and assault weapons.  These weapons will often send bullets completely through the target and can cause cavitation (nasty large exit wounds).  Remember that D&D heroes are mythically endowed with the ability to survive real-world damage so we aren’t trying to guarantee a kill.

Key characteristics:

  • Weapon Type: Ranged
  • Weapon Group: Ballistic
  • Attack: DEX vs. Reflex
  • 4 damage dice
  • Property: High Critical

What’s Next?

Accuracy, Rate of Fire, Reloading, Damage, Smooth Bore, Rifling, Artillery, explosives, and More…

(Think this is all stupid and you can do it better?  Tell me I’m wrong in the comments section.)



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