HMS Apollyon Firearm Rules

Overview

This module adds firearms to an OD&D or Basic/Expert-adjacent chassis without simply declaring them better bows. Its explicit design target is tension: guns should feel dangerous and modern enough to matter, but limited enough that melee weapons, bows, cover, and ammunition management still structure play.

The rules accomplish this by combining three main levers:

exploding damage on maximum rolls
burst-fire logic that trades ammunition for multiple hits
a cover-and-saving-throw procedure for automatic weapons and shotguns

Core Mechanical Ideas

Exploding damage

Most firearms deal 1d6 per bullet, but maximum results explode. A 6 on damage rolls another die and adds it, continuing as long as maximum damage keeps appearing.

This means even a nominally modest weapon can produce sudden lethality without requiring a large default damage die.

Burst fire

Some firearms can convert one attack roll into multiple bullet hits. For every two points by which the attack roll exceeds the needed number to hit, another bullet in the burst strikes, up to the weapon's burst value.

Burst fire spends ammunition fast. The module uses ammo burn as the main balancing factor rather than pure accuracy penalties.

Cover-based auto-fire and shotgun procedure

Automatic weapons and shotguns often stop making normal attack rolls at all. Instead, the target saves versus wands or devices.

fail the save: take full or double weapon damage depending on weapon type
succeed: take half damage
take cover: reduce the result further, often to no damage on a successful save

This is the subsystem's strongest distinctive move. It makes cover the real defense against suppressive gunfire rather than armor alone.

Weapon Handling Logic

The article distinguishes firearm families by tactical role rather than catalog completeness.

Pistols

usable in melee more easily than longarms
less accurate at longer range
dual-wielding is possible but incurs escalating penalties

Black powder guns

strong opening shot
three-round reload cadence
often best as ambush or first-contact weapons

Revolvers and cartridge weapons

faster reload than muzzle-loaders
burst capability on some models
good for repeated short-fight output at the cost of ammunition

Longarms and rifles

better range profile
awkward in melee without bayonets
scoped rifles reward concealment and deliberate aiming

Automatic weapons and shotguns

strongest interaction with the cover/save procedure
capable of forcing movement or pinning tactical choices
best when the environment offers meaningful cover states

Balance Strategy

The module does not try to balance firearms by pretending they are just re-skinned crossbows. Instead it gives them clear strengths and clear liabilities.

Strengths:

high lethality spikes
usability by any class
good alpha-strike potential
strong suppression and anti-cover pressure

Liabilities:

reload friction
ammunition consumption
cover sharply reducing effectiveness
poor melee handling for many longarms

That is a sound old-school balance philosophy. The answer to guns is not a hidden math patch. It is terrain, logistics, reload time, surprise, and pressure.

Comparison Hooks

Compared to simpler firearm add-ons, this module is more procedural and more tactical. It cares about:

how many rounds a reload really takes
whether the target dove for cover
whether burst fire is worth the ammunition spend
whether a rifle is being used as a firearm or an improvised club

Compared to fully simulationist gun systems, it stays compact. It still fits inside an OD&D combat loop.

Referee Use

Use this module when you want firearms to:

change battlefield behavior around cover
create occasional brutal lethality spikes
feel materially different from bows and crossbows
support science-fantasy, post-collapse, or weird-industrial campaigns

It works best in games that already care about ammunition, positioning, reload windows, and environmental protection.

Sources

https://dungeonofsigns.blogspot.com/2013/12/simplified-hms-apollyon-or-od-gun-rules.html