I saw a post here a month or two back on the forum about the best way to approach playing/running a BC game, I believe it mentioned something about the system encouraging the GM to be less restrictive and to react to what the players wanted to do, but I could aso be mistaken. Does anyone remember something like that? Searches don't seem to be helping, nor looking in the past posts

Warning: Wall of Text!
But , if you are a Black Crusade GM, I strongly recommend you give it a read in its entirety.

Many people have remarked that Black Crusade is a "sandbox" RPG, meaning much of what the PCs do in their quest to complete Compacts is driven directly by the choices made by the Players. This is true. However, there has to be some structure, otherwise the general concept of Black Crusade as a RPG breaks down into…well…chaos.

There are two ways this can be approached:

• The Players decide what the Primary Objective of a Compact will be, and they (along with GM input) determine what Secondary Objectives will lead them toward the completion of the Compact, and what Personal Objectives might be achieved along the way that will benefit the individual PCs.

Or…

• The GM creates a number of pre-constructed Compacts. Each Compact is outlined in general terms: Primary Objective and Secondary Objectives. The Players (with input from the GM) then tweek these pre-constructed Compacts to their mutual liking, and decide what Personal Objectives they would like to achieve along the way.

I've been giving this a lot of thought recently. As I have all five Core Rules books available, I have been looking at Compacts through the multi-faceted lens of Black Crusade (Compacts), Dark Heresy (the rules for Contacts presented in the back of The Inqusitor's Handbook), Rogue Trader (Endeavors and Meta Endeavors), and Deathwatch (Missions and Turning Points), all with a view toward a long-running campaign (utilizing the Heretical Campaigns material presented on pgs 26-31 of the BC GM's Kit as a guide to "stretching out" Infamy gain). While doing so, I've come to the conclusion that a Compact can be more clearly defined by porting the terminology from the other lines into a Black Crusade Compact. Personally, I believe preparation for a game session is key to keeping a campaign interesting, and it is difficult at times to maintain continuity and pace when the Players throw a monkey wrench (or three) into the works, and having a Compact more clearly defined seems the best way to manage the potential "hazards" that might arise along the way. I'm not trying to imply Players intentionally sabotage games, but sometimes they can be so unpredicatable.
Also, as it seems it will be important throughout any Black Crusade campaign I run, I have been considering the "value" of souls, and this has led me to look more closely at the rules for Profit Factor that are presented in Rogue Trader. I won't expound too much on this topic as I want to stay within the bounds of creating Compacts, but there may be references to the concept throughout my sample Compact (below). In short, Influence (Dark Heresy: Ascension) is the Imperial version of Infamy, both used to determine status and power, and Profit Factor would be an abstract representation of a Heretic's/Warbands's individual/combined temporal and "otherworldly" wealth.

In conjunction with this Compact, it is recommended that GMs significantly reduce the number of Infamy points awarded for personal achievements. These awards are themselves unassociated with the Compact, and should not be confused with Personal Objectives. These awards come as a result of defeating significant opponents, memorable role-playing moments where the PC acts in accordance with his/her Prides, Disgraces, and/or Motivations, etc. Below are suggested three categories and their associated Infamy awards:

• Trivial +1
• Noteworthy +2
• Outstanding +3

For the purposes of this Compact:

• The rules regarding the increase of Infamy through the expenditure of XP do not change.
• The amount of Corruption that results from Failings does not change.

Here's a sample Compact born of my efforts:

Compact Scope-

• Enterprise: A grand scheme that might take years to come to fruition. It begins with the Warband (PCs) Calling to Convene on Kurse.

Primary Objective-

• To support the Severan Dominate's bid for secession from Imperial rule and turn it to the whim and will of Chaos Unaligned (the Compact is not dedicated to a specific Chaos Power). If successfully completed, this Compact will award each member of the Warband with +15 Infamy. Failure to complete this Compact will result in each member of the Warband gaining 10+d5 Corruption

Secondary Objectives-

• Gain access to Severan Dominate miltary and resource assets within the Periphery
• Clandestinely prepare the Periphery's infrastructure for usurpation
• Destabilize Imperial military support and resources within the Periphery
• Demoralize Imperial military and its support assets (the Imperial Church, the Adeptus Mechanicus) within the Periphery
• Deliver crushing defeat to Imperial miltary and its support assets within the Periphery
• Usurp governance of the Periphery, utilizing it as a base of operations from which to attack the Callixis and Scarus Sectors

GM Note to Players- To mollify Player concerns about reprisals from the Scarus Sector, it will be assumed the Scarus Sector has its own issues to contend with (perhaps the time line is slightly altered to coincide with the Helican Schism or some other political/military ruckus), and by the time the Periphery falls to Chaos it will be too late for them to mount anything other than a hasty defensive stance. Additionally, the Imperial Crusade within the Jericho Reach is fully invested and too entrenched to allow for a redistribution of support away from their endeavors. Reprisals from the Callixis Sector and bullish opposition from Waaagh! Grimtoof will be the primary concerns.

It is as this point the Players must choose the Annointed and consider what resources their PCs can muster. Looking through the Secondary Objective Endeavors may help the Players determine which PC can contribute best to each of the Secondary Objectives. Alternatively, the PCs could choose to "micro-manage" the Secondary Objectives by mustering resources for specific Endeavors within the various Secondary Objectives.
The ability to communicate with their resources over great distances with a relatively short response time, an extensive network of infiltrators, sabateurs, informants, and counter-agents, and some semblence of a fighting formation that can support Severan military efforts on key worlds within the Periphery are just a few examples. The ability to navigate meta-crisis politics (relevant Skills and Talents) may also prove a boon, for the Warband don't want the Severan Dominate wasting their resources needlessly against Waaagh! Grimtoof if instead a clash with Imperial military assets might be orchestrated. The key to success is planned response, not hasty reaction.

At any time during this Compact the Annointed may abdicate his/her authority (gaining 4 Corruption) and another must take the reigns.

Enduring Complication- Waaagh! Grimtoof: Whether for "comic relief" or because the Warband are having too easy a go of the Compact, the GM is encourage to (infrequently) insert elements of Waaagh! Grimtoof as an inconvenient and reocurring Complication with inexplicably poor timing.

Regarding Secondary Objectives- Each Secondary Objective is either Trivial, Noteworthy, or Outstanding, and will involve the completion of one or more Endeavors, as follows:

Gain access to Severan Dominate miltary and resource assets within the Periphery-

• This is a Noteworthy Endeavor
• Embark on an embassadorial Endeavor to open dialog with Severan XIII. This may require the Warband to secure transportation through Imperial-held space (see Hand of Corruption for inspiration), and is a great opportunity for RP and Social Interaction Skill Tests/Talents (demagoguery) and a chance for the Warband to recruit personal Minions and allies to their Compact
• Negotiate a (seemingly) mutual beneficial arrangement. The promise (on loan) of advisory and military support (specifically targeted toward Imperial pressure). This allows the Warband to install their first tier of infiltrators, and shows the Severan Dominate the Warband are prepared to support their military with a private army/hired mercenaries in return for something (seemingly) reasonable (perhaps settlement rights to Sleef and Deluge)
• If negotiations are favorable, perpare to transport and deliver promised advisory staff (tacticians, negotiators, logi) and fighting formation(s). If negotiations fail, the only real loss (from the outset) is preliminary infiltration; perhaps the Severan Dominate just need proof of the Warband's sincerity?
• Possible Mishap/Setback- Nuisance (Minimal-level threat to the completion of the Objective): Dark Eldar interference; failure to resolve this effectively results in the Annointed permanently reducing his/her Infamy by 1 point
• Endeavor Infamy Reward: +1-3 points, depending upon the level of success toward completion of this Endeavor

Note: The last two bullet points in this Objective are to be kept secret from the Players.

Clandestinely prepare the Periphery's infrastructure for usurpation-

• This is a Trivial Objective
• If the Warband have successfully installed their first tier of infiltrators, they may begin the work of subverting governing policies, the military, economic trade and banking interests, and organizational institutions within the Periphery to their own ends. Otherwise, they may need to invest personal attention to this aspect of the Endeavor. Perhaps they first concentrate on the infiltration of sub-sector communications, replacing Astropathic Choirs with their own sorcerous cabals to the result of controlling and censoring information within the sub-sector and beyond? Also, clandestinely divert economic, military, and raw resources to their own purposes. The PCs may need to pool their Skill/Talent resources and recruit additional Minions in order to manage the logistical organization of a sub-sector
• Clandestinely fund raids on key worlds within the Periphery (perhpas negotiating a temprary arrangement with the meddlesome Dark Eldar, or recruiting Loxatl mercenaries) with the intent of installing "complimentary security forces", effectively usurping law enforcement in perparation for the Warband's coup at the climax of the Compact (the Dark Eldar would need to be weened from the agreement…if they don't betray it beforehand, wheras Loxatl mercenaries can be retained for use in future Endeavors)
• Possible Mishap/Setback- Grim (Medium-level threat to the completion of this Objective): The Dark Eldar predictably renege on their arrangement with the Warband, taking advantage of the confusion to raid the Warband's resources, destablizing their installment of "complimentary security forces"; the PCs must invest in replacements for the resources they dedicated to usurping law enforcement on several key worlds within the Periphery. Failure to resolve this effectively results in the Annointed permanently reducing his/her Infamy by 1-2 points, depending on the Warband's response time and whether the supicions of Severan XIII are raised. (possible Profit Factor reduction of d5 points representing both a wasted investment and associated replacement costs)
• Objective Infamy Reward: +1-2 points, again depending upon the Warband's response time and damage control

Note: The last two bullet points in this Objective are to be kept secret from the Players.

Destabilize Imperial military support and resources within the Periphery-

• This is an Outstanding Objective
• This Objective requires a siginificant initial expenditure of Profit Factor [20], but if successfully completed the Warband will recuperate their investment and net a bonus Profit Factor of 5+d5 points
• In order to destabilize Imperial military support and resources within the Periphery, the Warband have decided to commit a better portion of their own wealth and resources to a two-pronged assault on Imperial-held interests: pillaging the Forge Worlds of JXMA18Z and Synford II. With these Forge Worlds laid low and plundered the flow of replacement parts and supplies to Imperial military assets within the Periphery will grind to a trickle. Additionally, as an added hinderance to Imperial supply, the Warband will arrange for the major Warp routes connecting key worlds within the Periphery to the Callixis and Scarus Sectors to be relentlessly preyed upon by the aggressive Reavers of the Saynay Clan.
• In recruiting the Saynay Clan into this Objective, the Warband likely would have to offer something of significant value up front, with a promise to heap more onto the pile after the assaults on both Imperial Forge Worlds have been resolved. What they Clan wants as a "downpayment" for their services can be discussed between the Players and the GM: perhaps they want two Idolator-class Raiders, or perhaps they want food (10,000 convicts from the Prison World of St Annard's Penance; see Hand of Corruption). The Warband can "sweeten the pot" after the dust has settled by subtracting 2 Profit Factor from their Temporal Reward (see below)
• The Warband will need significant military might, transportation, and orbital support to take on not one, but two Forge Worlds. The PCs might liberate the entire prison population of St Annard's Penance with an eye toward using them as their primary military force (approx 15,000,000 men and women), and Chaos Space Marine PCs might be able to entice (with promises of glory) former associates to act as commanding officers and "heavy hitters" of the infantry assault. The Warband could attempt to recruit an armada of nefarious Rogue Traders/Corsairs at Kurse (see Hand of Corruption) or Footfall to transport their ragtag legions and act as orbital support in the planetary assault. This Endeavor could be expanded to include 10-12 individual "lesser" Endeavors all aimed toward the completion of one goal: looting two Imperial Forge Worlds. Hand of Corruption will be an invaluable resource when planning the liberation of St Annard's Penance!
• This Objective might include just one mass combat-themed Endeavor, one where the PCs are leading the assault on one Forge World, with the inclusion of 3-6 Turning Points (see Deathwatch) that directly influence the outcome of the mass combat and plunder ocurring on another Forge World. The mass combat rules in Tome of Blood will be useful when running this Endeavor; bring home the horror of mass combat in the 41st Millennium! GMs with Rogue Trader and Battlefleet Koronus might find this an opportune time to introduce their Players to ship combat in the void. Suggested Turning Points: Taking Control of Orbital Defense Platforms (frees infantry for deployment to the planet's surface with little-to-no orbital bombardment); Taking Control of AFV Manufactoria (prevents AdMech from committing more AFVs to the conflict, aleviating the infantry's disadvantage); Capturing the Core Cogitators (end-game of the assault, effectively dismantles AdMech's ability to coordinate their defenses and/or counterattack).
• Possible Mishaps/Setbacks (multiple, suggested 2)- Calamitous (High-level threat to the completion of the Objective): Communication discipline has broken down, or a suspicious message was intercepted from the warp- have several PCs with relevant Skills/Talents make Arduous Tests for the loyalty of their underlings and Minions, with a combined failure of 5 or more DoF resulting in word leaking to Imperial authorities regarding the imminent attack on the Forge Worlds. The Warband may need to scramble to misdirect or intercept the impending Imperial response, requiring them to act swiftly and personally. Further to this, the convict rabble that is their legion riots: have PCs with relevant Skills/Talents make Arduous Tests to Intimidate or Command the lot back into line (or there will be grave consequences; threats of voiding them into space gives one PC a +10 bonus to a single relevant Test), with a combined failure of 5 or more DoF resulting in the Warband needing to quash the riot swiftly and personally (several Hordes of 50-60 Magnitude within the confines of their transport vessels, though not all at once). Failure to resolve these issues effectively result in the Annointed permanently reducing his/her Infamy by d5+1 per Mishap. As this looks to be the first real "make or break" event in the Compact, the GM is encouraged to entertain any and all remedies the Warband conceive to get their legions back in line and deal with the communications leak, as it is in their very best interests to not let the Compact collapse at this juncture; fair GM discretion is essential.
  Diverting assets to misdirect or intercept Imperial response to the assaults will cost the Warband 10+d5 Profit Factor (quickly recruiting additional Saynay Reavers on short notice) or 30% of the combined forces committed to assaulting the Forge Worlds.
• Temporal Reward: As stated above, the Warband recuperate their initial investment of 20 Profit Factor and receive an additional 5+d5.
• Objective Infamy Award: Suggested 3-7 points. Additionally, each PC gains 5 Corruption (with an additional +2 if aligned with Khorne).

Demoralize Imperial military and its support assets (the Imperial Church, the Adeptus Mechanicus) within the Periphery-

• This Objective is Trivial
• The Warband must demoralize and humiliate Imperial Guard forces and the Imperial Church on key worlds within the Periphery, and cast a significant shadow of doubt on their decision to remain committed to the Spinward Front engagement. Apostates might rally the citizenry into open rebellion, or profane and reconsecrate Imperial churches and temples to the glory of Chaos Unaligned. Psykers and Sorcerers might unleash the hideaous powers of the Warp on their foes and scare the living saints out of them, blasting and breaking their minds and morale. Anything and everything the Warband can do to break down their convictions.
• The Warband must enact some sub-sector spanning ritual, complete with hundreds or even thousands of innocents sacrificed in blazing pyres, nothing supremely taxing, perhaps the summoning of small Hordes of Minor Daemons on three or four key worlds at one time (easy stuff for heretics).
• The Warband have to be careful not to overdo their reign of terror; arousing suspicions of the governing bodies of the Severan Dominate is likely to backfire.
• Possible Mishap/Setback- Grim: Through carelessness or overzealousness, Greater Daemons are summoned in place of Minor Daemons, and getting them under control or banishing them is of paramount importance. Daemons don't go quietly, and the PCs may be obligated to "cut them in" on the Compact… Failure to resolve this Mishap effectively results in the Annointed permanently reducing his/her Infamy by 3.
• Objective Infamy Award: 3 points, plus each PC who participates in the perparations and enactments of rituals gains 5 Corruption.

Deliver crushing defeat to Imperial miltary and its support assets within the Periphery-

• This Objective is Outstanding
• The end-game has come, and it is now or never. In one fell stroke, the Warband unleash the entirety of their allies upon the Imperial interlopers, driving them into the mud, delivering a crushing defeat and sending them in full retreat from the Periphery.
• Simultaneously and in perparation for their victory celebrations, the Warband begin a massive campaign of assassinations and take-overs that will leave the Severan Dominate reeling from the shock of it. Just as Severan XIII sees his independence on the horizon, the Warband gouge out his eyes and throw him to the beasts. The infrastructure of the Periphery is converted to the glory of Chaos Unaligned. Mass combat, glorious mano y mano, cold revenge, assassinations (perhaps even inter-Warband backstabbing?), monologues.
• Possible Mishap/Setback- Grim: Waaagh! Grimtoof chooses this very moment to step on the Warband's toes. The Orks refuse to give ground, taking and securing one of the Warbands intended "jewels of the realm", and the PCs must act with swift and ruthless brutality if they want to keep what is theirs by right of blood and toil. Mass combat. Failure to resolve this Mishap effectively results in the Annointed permanently reducing his/her Infamy by 1
• Objective Infamy Award: 3, plus each PC gains 3-7 Corruption (as a guide, those who held back and contibuted from the shadows until the dust settled gain 3, while those who risk all, including their souls, gain 7)

Usurp governance of the Periphery, utilizing it as a base of operations from which to attack the Callixis and Scarus Sectors-

• This Objective should be Trivial, but…
• The Warband consolidate their prize (logistics, organization, assassination "house cleaning")
• The Spoils are divided, each member of the Warband dedicating their share to the Ruinous Powers of his/her choosing
• Possible Mishap/Setback- Calamitous: Waaagh! Grimtoof takes this opportunity to capitalize on the Warband's glory intoxication. Poor consolidation of their remaining resorces (legions, transports, communication, infrastructure, etc) leaves the Warband backfooted, and they will have to fight tooth and nail for the capital world of the Periphery or be bashed aside by the brutish Greenskins. While massive forces clash on muddy, shell-hammered fields, the Warband leads an infiltration into the heart of Waaagh! Grimtoof's command in an attempt to establish just whose might makes right. Failure to resolve this effectively results in the failure of the Compact, and each PC gains 10+d5 Corruption
• Objective Award: Calculate Infamy and Corruption; Apotheosis, Spawndom, or Calling to Convene another Compact.

So, there you have a sample of a Compact of epic Scope. Obviously, if you wanted to use this particular Compact as it is presented you would have to have access to a great many of the 40K RPG publications. And I'd have to finish it… EDIT: I finished it.
This Compact can also be used as a template for those of your own creation.

When creating a Compact such as this, the Players (with input from the GM) are free to alter or change the Seconday Objectives and their associated Endeavors. Once those details are "hammered out", the Players can begin considering Personal Objectives for their individual PCs based upon their Prides, Disgraces, Motivations, and each Player's concept of their character, their "targets of opportunity.". (I also recommend taking a look at HappyDaze's House Rules that allow Players to choose Prides, Disgraces and Motivations that are free from game mechanic bonuses/penalties.)
Mishaps/Setbacks, penalties to Infamy, and Corruption for Failings would be kept secret from the Players. Essentially, the GM would have a "master copy" with all the technical bits (Rewards, penalties, Turning Points, etc), and the Players would each have a copy of the Compact's Primary Objective, the Secondary Objectives and any associated Endeavors, and possibly some sort of back-up (Plan B).
It is important to note that there is no strict order in which the PCs are to embark upon and complete their individual Endeavors, so long as they reasonably manage the completion of each Secondary Objective to time with the end-game. Tipping themselves to the Severan Dominate before they're within reach of the prize means a failed Compact, and the Warband do not want that to happen.

It would take considerable effort on the part of a dedicated GM to arrange and present two or three such Compacts to his/her Players, but I feel the benefit of time saved during actual campaign play would be significant; no panic or scramble, the GM can prepare many adversaries, encounters, and events in advance. And the Players will have a sense of working toward a clear Objective without "getting lost" along the way; a mutable screen play, if you will.

No idea. But BC isn't so far off of Rogue Trader in how many ways you can take the game. I mean, "Abbadon! Isha's escaped! Recruit Five Heretics with Attitude!" can actually be made viable, ya know?

Probably, the important factor in running BC is that as the "villains" your players can't just be reactive. A lot of settings make it easy to 'funnel' the party around: They're parts of a monolithic organization. Loyalty or death, duty or death, and the general guilty feelings of having let horrible things happen to a whole lot of slightly-less-guilty innocents go a long way towards making sure they generally go in the direction that you gave them. Sure, perhaps the way they get there is mindbogglingly unexpectable, but in general, overall, they'll end up where you think.

In Black Crusade, a lot of what the characters do is motivated by self-interest. What they need are points of interest, rumors, or even spreadsheets of hard data on population density in temperate mountainous regions of Planet X in System Y of Sector Z in order to make their decisions on what they should do next. And that's where it gets tough. What do they WANT to do? What are their character's ambitions? How do they plan to get there? If you can know these you can feed them what would get their characters attention.

Not kidding about the spreadsheets, either. Some folks are only spurred to action when they've got "I'm an accountant for my corp in EVE" stacks of bloody data, but if that's what gets the player into a galactic-domination-mood; and it probably will, then so be it. He'll probably have their primary compacts for the next 10 000xp planned out.

Either way, a lot of the game's planning has to be done on a reactionary level: "if they decide to go there, this is what's currently in the area, this is how they might respond if found/intercepted/interacted-with, and this is who is keeping an eye out for trouble over this". In a way, gm and players have their jobs reversed: They have to decide what the "villains" are up to, and you have to decide if the "good guys" will even figure out what's going on in time to try and stop them. Which can be fun but tedious: sometimes its worth figuring out what important NPCs are bound to miss or not give a crap about; perhaps a local commissar won't think twice about charging suspected mutants, but couldn't be arsed to lift his chainsword and order a raid on someone smuggling out amasec. Or perhaps a local arbiter has been doing rounds for twenty years because he doesn't have the mental capacity to do any real detective work.

Or perhaps today there's an inquisitor sniffing down their trails…