Firearms (5e Variant Rule)
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A collection of variant rules useful for modern and futuristic firearms.
Armor Piercing
Attacks with weapons or ammunition with the armor piercing property are quite effective against armor. Armor Piercing always overlaps with Armor Piercing of a lesser numerical value - for example, an Armor Piercing 2 weapon is also Armor Piercing 1, and as usual when effects of the same name overlap, the more powerful one applies. Armor Piercing X always counts as an effect of the same name with itself, so values on the weapon and ammunition overlap rather than stack.
Armor Piercing (1). +1 to hit against targets with natural armor or worn armor and an AC of 14 or better.
Armor Piercing (2). +2 to hit against targets with natural armor or worn armor and an AC of 16 or better.
Armor Piercing (3). +3 to hit against targets with natural armor or worn armor and an AC of 18 or better.
Because you generally do not know the AC of your target, express a hit roll with, say, an Armor Piercing 2 weapon to your target of, say, 18 as "18 to hit, Armor Piercing 2".
- Design Note
When designing weapons or ammunition, do not use the armor piercing property for attacks that would entirely ignore armor. Such a weapon would not use an attack roll at all: instead the target(s) would make some form of saving throw.
Burst Fire Nonproficiency
The DC of Dexterity saving throws made against firearms using burst fire (DMG p. 267) is 10 (not 15) if the attacker does not have proficiency with the weapon.
Burst Fire Proficiency
The DC of Dexterity saving throws made against firearms using burst fire (DMG p. 267) is 13 + the attacker's proficiency bonus (not 15) if the attacker has proficiency with the weapon. You may use this rule in conjunction with the Burst Fire Nonproficiency rule, above.
Hearing Distance
Firearms are very noisy! The following table gauges how difficult it is to hear a gunshot or explosion, by the size of a weapon. There are four brackets, each of which determine the DC of a hearing-based Perception check to hear a gun being fired. The first bracket ("Automatic") is the maximum distance within which a weapon is so loud, it's impossible not to hear it unless you are deafened. Within that radius, you do not have to make a Perception check to hear it; it is automatically audible. Further away, it is increasingly less certain; the next three columns give a DC which must be passed to hear the sound of a firearm.
| Weapon Type | Automatic | DC 10 | DC 15 | DC 20 |
|---|---|---|---|---|
| Suppressed or "Silent" Firearm | 60 feet | 120 feet | 240 feet | 480 feet |
| Light Pistol, Musket | 200 feet | 400 feet | 800 feet | 1,600 feet |
| Grenade Launcher1, Heavy Pistol | 400 feet | 800 feet | 1,600 feet | 3,200 feet |
| Rifle, Shotgun, Submachine Gun | 800 feet | 1,600 feet | 3,200 feet | 1 ¼ miles |
| Machine Gun, Stun (Nonlethal) Grenade | 1,600 feet | 3,200 feet | 1 ¼ miles | 2 ½ miles |
| Anti-Personnel Explosion, Grenade | 3,200 feet | 1 ¼ miles | 2 ½ miles | 5 miles |
| Anti-Vehicle Explosion, Tank Cannon | 1 ¼ miles | 2 ½ miles | 5 miles | 10 miles |
1This is the sound of a grenade launcher firing, not the sound of an exploding grenade, which is much louder (see further below on the table).
The DC of the Perception check assumes that the firearm is being used in a typical, relatively clear outdoors environment; the DC may be slightly lower when you are surrounded by stone or concrete (since those materials reflect sound, making it louder), or even lower in an enclosed space such as inside a building. On the other hand, the DC may be slightly higher in an environment such as a dense forest where there are many obstacles to diffuse the noise. Use common sense; it may be difficult to hear the sound of a pistol going off, even within the normally "automatic" distance (necessitating a Perception check), if there is a very loud background noise, such as heavy machinery or fireworks.
Short Burst
Firearms with the short burst trait can, fire a number of rounds of ammunition with a single pull of the trigger. This is typically a three-round burst but could be anywhere between two and five.
When you make an attack with a firearm with this trait, you can choose to expend a single round of ammunition as normal, or fire a short burst and expend additional rounds of ammunition as indicated in the parenthesis. If you fire a short burst and successfully hit, you can re-roll a number of the damage die, as indicated in the parenthesis, accepting the new results.
For example, a bolter has short burst (2), so when you attack you expend three rounds of ammunition and re-roll two of the damage die if you successfully hit.
Scope
Firearms with the scope trait have a scope which facilitates extreme long-range engagements.
If you have not moved since the end of your last turn, you can use an action to aim down the scope of a firearm that has this trait at a specific target. Once you do so, you are incapacitated and your speed becomes 0 until the start of your next turn. However, the first attack you make against the target at the start of your next turn is made as if the firearm has a different range value (listed in parentheses), with no long range at which attacking imposes disadvantage on your attack roll.
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