Guide — OPR Sim

Field manual

Reading the sim

OPR Sim answers one question exactly: if this unit attacks that unit once, what happens? Everything on the page is either an input to that question or a way of reading the answer. This guide covers both, then the two rules editions you can ask it under, and then the tag system that helps you find the unit you're after.

What it computes

The sim walks the OPR combat sequence for every weapon in the loadout and computes the full probability distribution directly: no dice are rolled, so the numbers are exact and identical every time.

01QualityEach attack die hits on the unit's Quality or better. A natural 6 always hits, a natural 1 always misses.
02BlastBlast(X) turns each hit into X hits against a unit with at least X models.
03DefenseThe target rolls Defense per hit, minus the weapon's AP (summed across rules). Cover adds +1 against shooting.
04WardRegeneration and wards ignore a failed save on a roll; Bane, Rending and Poison switch some of that off.
05WoundsDeadly(X) multiplies each wound. A model dies after taking its Tough value; leftover damage carries to the next model.

The result panel

Models killed: The expected number of models removed, wounds pooled across weapons and floored by Tough the way you'd allocate them on the table.
Wounds dealt: Expected damage points into the unit's wound pool, capped at what the unit can absorb.
P(wipe): The probability every model in the target is destroyed. This is the number to look at for "will it die", not the average.
Distribution: The bars show how likely each outcome is. A wide spread means a swingy attack; the average alone hides that.
Per-weapon breakdown: Each weapon's hits and wounds on its own, so you can see which upgrade is actually earning its points.
Pin to compare: Freezes the current matchup in the compare strip. Pin a few loadouts or targets side by side to see what changes.

Setting up a matchup

Each side is a panel: game system, faction, unit. The attacker's loadout and the fight's context live under it.

Loadout: Every weapon the unit carries, toggleable. Upgrades opens the unit's ArmyForge options; taking one swaps or adds weapons and rules exactly as the list builder would, priced per unit. The header total shows base + upgrades + attached hero.
Models firing: Scales the unit's dice for a depleted squad. Combined unit doubles a multi-model unit (OPR's combined-units rule).
Attach hero: Joins a Hero to the unit: its weapons fire alongside, its auras apply, and as a defender its Tough sits at the end of the wound pool.
Phase & context: Shooting or melee; charging (enables Impact, Furious, Lance); fatigued (hits only on 6s); range over 9" (Relentless, Stealth); cover (+1 Defense vs shooting).
Applied effects: Every army-wide buff or debuff the book defines, as a toggle. Nothing is rolled: switch one on to see what it would be worth if it were active.
Spells: Damage spells are added as an attack weighted by the chance to cast at the chosen token count; buff and debuff spells mix the buffed and unbuffed outcome by that same chance.
One-off abilities: Breath, Storm, Self-Destruct, Dangerous Terrain and the like: opt-in, since they don't fire every activation.
Counter & reflected damage: A defender with Counter strikes first when charged; Retaliate and Deathstrike bounce damage back. Both appear as their own readouts when they apply.

Rules editions

The switch in the header picks which rules you are theorycrafting under: 3.5, the published game, or 3.6 beta, OPR's v3.6 open beta. It changes everything downstream — the army list, the units, the weapon profiles, the points, and how the fight is resolved. Each edition remembers its own matchup and its own pins, so flipping across and back leaves your work where it was.

A BETA marker rides along wherever beta numbers are on screen. Take them as provisional: the beta armies are a snapshot from September 2026, and OPR is still re-pricing and re-wording units while the beta runs.

What 3.6 changes in the math

AssaultAn Assault weapon counts as both a ranged and a melee weapon, so hybrid guns fire in either phase.
ImpactImpact hits resolve before either side strikes, instead of alongside the charge. Counter no longer reduces them — Brace(X) does, and only in fantasy.
OverrunVehicles trade Impact for an Overrun melee weapon with Thrust.
ParryParry(X) is a ward against melee wounds: each one is ignored on a 6.
FatigueA fatigued unit hits only on 6s, and its effects that trigger on a natural 6 are switched off.
IndirectIndirect weapons no longer take a penalty for having moved.
AircraftShooting at an aircraft is -1 to hit, and aircraft weapons have half the range they used to.
SergeantIn fantasy, a Sergeant adds AP(+1) instead of an extra hit on natural 6s.
Over 12"Entrenched and Artillery now ask whether the target is over 12" away instead of over 9". The range switch stands in for that.
UnchangedThrust, Lance, Surge, Shred, Blast, Rending, Deadly and Regeneration work the same in both editions.

Two more context switches

Several 3.6 army rules used to key off distance and now key off the turn order instead, so the context row gains two switches under the beta:

Target already activated: The unit you are shooting or fighting has already gone this round — what the rules that reward hitting a spent unit look for.
Defender already activated: The same question asked of the defending side, for rules that only bite while the defender still has its activation in hand.

Skirmish armies are their own armies

In 3.6 the skirmish-scale games do not share unit stats with their parent game: Firefight and Age of Fantasy: Skirmish list tripled Tough, doubled attacks and their own points (600 and 800 pt standard games), and Age of Fantasy: Regiments words Impact, Parry, Brace and its spells its own way. Under the beta switch those are separate armies rather than the same book read three ways, so picking Firefight gives you Firefight's numbers, not Grimdark Future's.

Weapons were re-worked and re-named across the board in the beta, hybrids are handled by Assault, and "all models" upgrades now read "most models". Casters can also buy a Spell Amplifier for +1 to cast.

Unit tags

Under a unit's stat chips sits a row of pills. They are an interpretation of the unit, not a rule from the book, and they come from two sources. The colour tells you which.

Judged from the text

Role and range are decided by an AI that reads the unit's stats, weapons, rule text and points and picks from a fixed list. It reports how confident it was; a split decision shows both candidates with a hollow marker.

Computed from the numbers

Archetype, defense class and mobility are arithmetic: the sim shoots every unit at a set of reference targets and ranks the results within its army book. No judgement involved.

Role

What the unit is for. One per unit, chosen from:

Anti-infantry: Built to kill many low-toughness models: lots of attacks, Blast, little AP.
Anti-tank: Built to kill single tough targets (vehicles, monsters, heroes): high AP, Deadly, Rending, big Impact.
Tarpit: Numerous or tough for its points; ties enemies up in melee and soaks attacks rather than dealing damage.
Objective holder: Durable and/or numerous; its job is to sit on objectives and survive.
Hero support: A Hero whose value is joining and buffing a unit, not its own damage.
Caster: A spellcaster whose main value is casting spells.
Artillery: Long-range or indirect fire support; sits back and shoots.
Transport: Primarily carries other units.
Generalist: No dominant role; solid at several things.

A role under 50% confidence is shown as "A / B" and matches both filters. Hover or tap any pill for the confidence and runner-up.

Range

Melee: Deals most of its damage in close combat.
Short range: Deals most of its damage with shooting up to about 12".
Long range: Deals most of its damage with shooting at 18" or more.

Archetype

A list-building label that falls out of two numbers per point spent: damage (expected wounds per 100 pts into the reference targets below, best phase) and durability (AP(1) hits needed to wipe the unit, per 100 pts, wards included). Both are ranked as percentiles within the unit's own book, then:

Hammer: Top-quartile damage per point in its book: a unit you build the list around.
Anvil: Top-quartile durability per point with below-median damage: holds the line.
Glass cannon: Top-30% damage per point but bottom-quartile durability: hits hard, dies easily.
Chaff: Cheap bodies: 5+ models at 15 pts/model or less, without standout damage. Screens, blocks charges, soaks fire.
Balanced: Middle of the pack on both damage and durability per point.

The pill's tooltip shows the actual percentiles, so you can see how close the call was. A unit that is top-quarter on both damage and durability reads as Hammer; damage wins the tie.

Defense class

What the unit is as a target: the OPR equivalent of GEQ / MEQ / TEQ, read from Defense and Tough.

Light: Defense 5+ or worse, 1 wound per model. Dies to volume of fire.
Medium: Defense 4+, 1 wound per model.
Armored: Defense 3+ or better, 1 wound per model (marine-equivalent).
Elite: Tough(2–5) per model: multi-wound infantry, cavalry, bikes.
Heavy: Tough(6–11): heroes, beasts, light vehicles.
Tank: Tough(12–17): tanks, monsters, walkers.
Titan: Tough(18+): titans and super-heavies.

Mobility

Movement traits read straight from the unit's rules. A unit can carry several.

Fast: Moves 9" / 18" instead of 6" / 12".
Flying: Moves over units and terrain.
Aircraft: Flies 36" in a straight line; enemies get -1 to hit it; cannot hold objectives.
Ambush: Can be held in reserve and deployed anywhere over 9" from enemies.
Scout: Moves 12" after deployment, before the game starts.
Slow: Moves 4" / 8".
Immobile: Cannot move.

Reference targets

The five stand-ins every unit is shot at to compute its damage numbers:

target	models	defense	tough
light	10	5+	1
MEQ	5	3+	1
elite	3	2+	3
heavy	1	3+	6
tank	1	2+	12

Finding units

The unit picker is a finder. Type a name or a tag word ("caster", "ambush", "glass cannon") into the search box, or click facet pills. Role and archetype are always shown; defense, mobility and range sit behind more.

Within a group: Pills are OR: Anti-tank + Artillery shows units that are either.
Across groups: Groups are AND: Anti-tank + Fast shows fast anti-tank units only.
Dimmed pills: A pill that would leave nothing given your other filters is dimmed rather than a dead click.
The count: "8 / 26" is matches over the book's units. The dropdown lists exactly those, and picking a filter that excludes your current unit jumps to the first match.

Caveats

The beta is a snapshot: The 3.6 armies were read from the open beta in September 2026 and do not update themselves. Points and wording will change before v3.6 is published, so use the beta side to see where the edition is heading, and the 3.5 side for a game you are actually playing.
Tags follow the loadout: Archetype, defense class and mobility are recomputed on the spot for whatever you've selected, so a tank that buys laser cannons moves to Hammer as you click. Role and range were judged in advance for the base unit and for each single weapon upgrade; with several taken, the priciest one's judgement is shown, and the tooltip says which.
Relative to the book: Archetype ranks are within the unit's own army. An Anvil in a fragile army is not as tough as an Anvil in a marine book.
A reading, not an oracle: Role and range are an AI's reading of the unit's text. It is good at "what is this for" and is asked nothing numeric; where it was unsure, the pill says so. Trust the sim's numbers over any tag.
Not win rates: Nothing here comes from tournament results. It is the math of one attack, and the tags are a way to navigate it.
Fan tool: Stats come from ArmyForge; rules and names belong to OnePageRules. If something looks wrong, the per-weapon breakdown usually shows why, and support@juneaulabs.io hears about the rest.

← back to the sim