Tag: firearms

Complex Firearms for D20 Games

Public domain photo. Source: https://www.pikist.com/free-photo-sjtuq

There are several concepts that need to be understood for proper potential damage dice for a given firearm system. There are two kinds of cavities that are created when a projectile hits a body. The wound cavity is created by the track of the projectile damaging tissue as it travels through the body, creating a hole or tunnel as it goes, and in some cases creating multiple tunnels of damage if it fragments. The second is the Stretch cavity which is created when the shockwave of the projectile hits the body and moves tissues around like throwing a rock into a pool of water. For handguns, there are many impressive gel tests that show very dramatic stretch cavities using slow motion video. However the stretch cavity does not actually damage any tissue. Only the wound cavity damages tissue. Tissue damage causes bleeding, and when there is enough blood loss, the target is stopped. Larger projectiles make larger holes and thus more blood loss potential.

The shock of the stretch cavity can, in rare cases, cause enough shock to the nerves that it can render the target unconscious. Hydrostatic shock, where the stretch cavity actually causes tissue damage, does not occur with any tissue damaging results unless the projectile has enough foot-pounds of energy when it strikes the body, depending on the size of the body being hit. Energy is mass times velocity squared. Heavier projectiles have more mass, but require more pressure to give them velocity. The smaller the target, the larger the stretch cavity, the more potential for hydrostatic shock. This is not easy to translate into game terms. However, as a general rule, in Tiny targets, Firearms always product Hydrostatic shock. In size Small, 400 foot-pounds of energy would be needed to create hydrostatic shock (in hunting terms, this would be Class I game—Rabbits, Badgers, Coyotes, Antelope, etc.). In size Medium, 700 foot-pounds of energy would be needed to create hydrostatic shock (Class II game—Cougars, Deer, Antelope, Black Bear, Humans, etc.). In size Large, 1200 foot-pounds of energy would be needed to create hydrostatic shock (Class III game—Brown Bear, Mountain Sheep, Elk, Caribou, Moose, etc.). In size Huge, 1200 foot-pounds or more energy would be needed to create hydrostatic shock (Class IV game—Elephant, Hippo, Dragon, etc.)

The next issue is entropy; the projectile slows down, thus reducing its energy, as it travels. All Centerfire Rifles do Hydrostatic shock (unless they are chambered in a pistol cartridge) at under 100 yards. Some handguns under 30 feet can also do it. Beyond 100 yards, it depends on the cartridge being used (higher pressure has more velocity; heavier projectiles have less velocity but more mass) and the barrel length (the longer the barrel the more velocity). Things like barometric pressure, elevation, and so forth also play a role in the velocity of the projectile, and therefore the energy of the projectile when it impacts its target. The further out a target is, the less energy the projectile has to apply to the body. The furthest away, unless using specialty optics, that a good shooter can shoot effectively is 1200 yards. Game hunters and guides recommend you not take a shot with any standard cartridge rifles at anything further out than 400 yards. In order to have a humane kill, the magic number is 1200 foot-pounds of energy. If your platform and cartridge being used can’t produce that at the range you are considering taking the shot at, don’t take the shot.

There are literally thousands of developed loadings for a given cartridge. To simplify things, though, there are three basic bullet types: Standard loading for most cartridges is a full metal jacket bullet. Expanding, in most cases, is a jacketed hollow point or soft point round. Armor penetrating is typically an iron core round. The standard loading is assumed in the following pages. Expanding bullets will do an extra die of damage in exchange for a 25% penalty to the Accuracy Range increment. These are usually ‘defense’ rounds in Handguns. Armor Penetrating adds a bonus to hit to represent the negation of armor class and an identical penalty to damage to reflect the energy lost punching through the armor. In most cases, a flat +4 to hit and -4 to damage should be assessed. If the armor has a Damage Reduction rating (DR), you ignore it. Yes, they are nasty! But they are also dangerous, as they ignore Hardness of objects. Don’t use them inside a space ship!

Taking all these factors into consideration, we can lay some ground rules in determining weapon damage for Firearms in simple fashion. First, Rimfire Rifles, Black Powder, Pistols, Shotguns, and Centerfire Rifles have different pressure thresholds, and so they are separated. Rimfire uses a flash compound in the rim of the case that ignites the powder. Because of this, the weaker case does not allow for higher pressure. Centerfire uses a primer cup held in a primer pocket in the case. This allows for much higher pressure. Black Powder doesn’t use primer at all. Second we can simply utilize generic data on cartridges in “standard” platforms for that cartridge off Wikipedia.

What follows is a “simple” way to determine damage and range for a given “standard” platform for a given firearm cartridge using Pathfinder Second Edition rules. I took the “normal” top and bottom end cartridges to calculate the range increments and rounded the numbers off to make is simpler. There are more powerful, and less powerful, guns than what I used to determine the mean, but I kept it to what would be considered common firearms. For example a 500 S&W Magnum does 5000 J of energy out of pistol, and a 50 BMG rifle does 21,000 J of energy… and they cost between $5 and $20 per shot to fire… so they are not very common, and really mess with the numbers if you include such beasts.


All Firearms have a Damage Range increment, in addition to the normal Accuracy Range Increment other ranged weapons have. The Accuracy Range increment can be improved with the use of an Optic system.

Firearms Range Increments, Table 1

Weapon Type Accuracy Range Increment* Damage Range Increment
Centerfire Rifle 300 feet / 100 m 300 feet / 100 m
Rimfire Rifle 150 feet / 50 m 150 feet / 50 m
Handguns 75 feet / 25 m 30 feet / 10 m
Shotguns (scatter) 50 feet / 15 m 10 feet / 3 m
Smoothbore Black Powder guns 75 feet / 25 m 30 feet / 10 m
Rifled Black Powder guns 225 feet / 70 m 50 feet / 15 m
Black Powder Scatter guns 50 feet / 15 m 10 feet / 3 m

At the first Damage Range increment, damage is normal. But for each Damage Range increment out, the firearm does one damage die less. If it is down to its last die, the die type reduces by one die type for each Damage Range increment after that; with a minimum of 1 damage.

*Hollow point and soft point bullets give a 25% penalty to the Accuracy Range Increment

Optics

A Scope adds the Volley 30 trait to the weapon. In Pathfinder 2e terms, you have a -2 penalty to use the gun if your target is within 30 feet / 10 m of you. The Accuracy Range Increment is increased by 33%.

Red Dot systems do not impose the Volley penalty, but only increase the Accuracy Range Increment by 10%.

Optics may also grant features such as night vision or recording capabilities, depending on the system used.


The bigger the caliber of projectile, the larger the wound cavity, reflected in a larger damage die size:

Firearms Damage Dice, Table 2-1

Imperial Caliber Metric Caliber Damage Die
.17 – .236 4.318 – 5.994 d4
.237 – .302 6.02 – 7.671 d6
.303 – .368 7.697 – 9.347 d8
.369 – .434 9.373 – 11.024 d10
.435 – .50 11.05 – 12.7 d12

Most black powder pistols are .36 or .45 caliber (d8 or d12). Most black powder rifles are .45, .50, or .58 caliber (d12).

 The higher the energy, the more dice are rolled:

Rifle Damage Dice, Table 2-2a

Energy in Joules Dice**
< 2000 J 2d
2000 J / Black Powder 3d
3000 J 4d
4000 J 5d
5000+ J 6d

Pistol Damage Dice, Table 2-2b

Energy in Joules Dice**
< 300 J 1d
300 J 2d
500 J / Black Powder 3d
900 J 4d
1300 J 5d
1500+ J 6d

** Expanding bullets get an extra die of damage.


Shotguns shoot multiple projectiles and are treated differently as they are designed for short ranges, and therefore the size of the shot determines the number of dice:

Shotgun Damage Dice, Table 2-3

Shot Size Dice
#000 Buck 5d12
#00 Buck 5d10
#0 Buck 5d8
#2 Buck 5d6
#4 Buck / Black Powder Scatterguns 5d4
#5 Shot 4d4
#7½ Shot 2d6
#8 & #9 Shot 1d6

If only one die is being rolled, it may ‘explode,’ meaning that if the highest possible result is rolled, the die is rolled again, and the result is added to the original roll. This can continue until the highest possible result is not rolled.


To determine the damage and range of a specific gun, we simply look up a cartridge on the Wikipedia and compare its caliber, type (centerfire, Rimfire, or handgun) and energy. Use the highest rated energy loading on the page. For example, I’ll look up 7.7×58 Arisaka on Wikipedia. It has a diameter of 7.92mm. It’s highest rated energy listed is 3136 J. So looking at our lists above, it uses 4d8. Not too shabby. So instead of creating long laundry lists of damage, we’ve created a formula to convert any firearm to Pathfinder 2e damage.


Here are some more common cartridges converted:

A standard 5.56 NATO (AR15/M16) would use d4s, and at 1859 J it gets 2 of them (they can also fire .223 Remington at 1814 J, still only 2 dice).

A 9×19 Parabellum (9mm, 9mm Luger) +P Pistol uses d8s and at 617 J uses 3 of them. This covers the Beretta M9 (FS92), the standard NATO side arm from 1985 until 2017. Also the Sig Sauer P320 (RX17) from 2017 to Present. It is the most popular round next to .22 Long Rifle. The Glock Model 19 is the most popular handgun in this cartridge. Portland Police use Glock Model 17, as do all Federal Agencies except the Border Patrol and NCIS.

A .357 Magnum Pistol uses d8s and at 964 J uses 4 of them. Examples include the Smith & Wesson Model 27/28, Colt Python, and Ruger Security Six. A lot of State Police agencies and the Border Patrol switched from S&W 10s to S&W 28s in 1955 and used them until 1992.

A .357 SIG Pistol uses d8s and at 978 J uses 4 of them. The Glock Model 31 is the standard U.S. Border Patrol and NCIS sidearm.

7.62×39 (AK47/SKS) Rifles use d8s (0.310 caliber projectiles) and at 2108 J uses 3 of them.

The .38 Special +P Pistol (S&W Model 10 was the standard Cop gun from 1899 until 1990) uses d8s and at 476 J gets 2 dice.

The .40 S&W Pistol uses d10s and at 797 J uses 3 of them. Most cop guns are Glock Model 22.

.45 ACP (Colt 1911) uses d12s and at 796 J uses 3 of them. This was the U.S. Forces Pistol from 1911 until 1986 with 8+1 rounds. A smaller 6+1 round Officers’ version was carried by U.S. Forces Officers from 1955 until 1985. A 7+1 Round Commander version was available for Civilians.

A .270 Winchester rifle uses a d6 and at 4006 J uses 5 of them.

30-06 rifle uses d8 and at 4042 J uses 5 of them.

M1 Garand is a 30-06, but must be loaded to under 2800 J so they get 3 dice (use of regular 30-06 ammo will blow the op rod off the gun and damage it).

7.62×45 NATO rifles (M14) use d8s and at 3560 J uses 4 of them (they can also fire .308 Winchester at 3700 J, but still only 4 dice)

.22 Long Rifle in a Rifle gets d4s and at 277 J gets 2 of them, but only 1 in a Pistol.

Note: There are more powerful guns, but this keeps them capped for playability.


Additional Rules

Report Shock: When you fire a firearm without a suppressor, Report Shock takes place. The rules may vary depending on the game system, but by and large, if you are within 25 feet of the muzzle of an unsuppressed firearm, you must make a Fortitude, Constitution, or equivalent saving throw. In Pathfinder 2e, it would be a Simple DC for your level at Good Difficulty. If you succeed, nothing happens. If you fail, you take 1d8 points of non-lethal damage, and are both deaf and stunned for one round. If you are already deaf or have hearing protection in place, you are immune.

Overpenetration: If a target’s hit points are reduced to zero and there is still damage left over, the bullet “blows through” the target and may strike a creature or object behind the target. The original attack roll is used to see if the round hits, and if so, the remainder of the damage roll is applied to that target.

Recoil: Modern and Black Powder Firearms generate Recoil after each shot. A cumulative -1 penalty to hit is applied per shot fired to the next shot. This lasts until the shooter takes the Readjust action, Moves, or performs some other Action other than firing the weapon. However, Firearms are Agile weapons. In Pathfinder 2e, Recoil offsets the Agile trait when doing a multi-attack. If you do not do some other action prior to firing, the penalty continues to accumulate across combat rounds.

For instance, in Round 1, you fire three times. The first shot has no penalty. The second is at -5 (-4 for an Agile weapon and -1 for Recoil). The third shot is at -10 (-8 for Agile weapon, -2 for Recoil). In Round 2, you keep firing. The fourth shot is -3 for Recoil. The fifth at -8 due to -4 Recoil and -4 Agile weapon. The sixth is -13, and so forth. In Round 3, you take the Readjust action, which clears the Recoil penalty.

Reloading: Reloading is an Interact action and may require more than one action, depending on the weapon system being used. Most magazine-fed systems take two actions to reload: one to draw the magazine while ejecting the old one, and one to load the magazine and charge the weapon system.

Non-detachable magazine systems take a number of actions equal to 2 per cartridge being loaded, as do swing-out revolvers when not using a speed loader. Using a speed loader device takes only 3 actions to reload. Single Action Revolvers take an additional action per cartridge to eject spent cartridges through the load gate.

Modern single shot systems take three actions to reload: One to eject the spent cartridge, one to ready the new cartridge, and one to load the cartridge.

Black Powder weapons take 10 actions to reload. This time is cut in half if they have pre-measured powder wraps and a wad and ball block. Paper cartridge and cap & ball weapons take five actions to reload per chamber. Non-cap (primitive) Black Powder weapons such as wheel-locks take an additional two actions to ready the pan unless the user employs a single-action fire ability or spell to ignite the pan.