Just curious as I don't own all the books in every game system for Warhammer 40K RPG's yet:

Are the combat rules and vehicle rules the same in each one?
I've been looking over a friend's copies of his Deathwatch set, and the vehicle rules look exactly the same (comparing Rites of Battle and Into the Storm).

Not so sure about combat (basic, not starship), but it looks almost the same on a casual look between the two core rulebooks for both systems.

If they mesh together well enough, would be a good incentive for me to start collecting the Deathwatch line and GM'ing it, rather than just sitting in on games run by others.

If anyone wants to do a comparison of those two with Dark Heresy, I'd be interested in hearing it as well.

Not too worried about Black Crusade yet.

The basic system is pretty much the same, but there are slight differences in the way certain talents and weapon properties work between systems (not to mention the fact that the generic patterns for weapons can differ between the different lines). The overall intention when Black Industries first announced the line (which FFG have done a pretty sterling job of upholding, considering) is that it should be possible to play a single character all the way up through the various games, with each new one being a different tier of ability. The biggest issue that could crop up, offhand, is reconciling the psychic systems (if you're going to mix'n'match), and that a character built using one of the 'lower tier' systems will be capable of a far broader range of things when advanced to theoretical parity with one built using a 'higher tier' system. Gear should translate pretty well from one system to another (and I have a standing rule that players can 'port whatever DH gear they want into RT, provided they come up with a justification for it, and ask my permission first if it's from the Ordos, high Mechanicus or anything from Ascension).

If you aren't bothered about mashing the systems together, but are thinking of running multiple separate campaigns, you'll probably run into more snags: as I said, the basic underlying system is fundamentally the same between DH, RT and DW (don't have BC yet myself, only skimmed it in the store), but there are a number of minor tweaks you'll come across which alter how the game works. Not generally game changing, but they seem to be made to tighten how the rules work with the differing scale and (more importantly) emphasis of the games. Mixing systems isn't too bad, as long as you pick whichever one you're going to use as the "base", but switching between and you'll run into minor, but jarring, snags as you realise that a particular mechanic doesn't work that way in this game.
I'd throw out specific examples if I were more awake, but since I'm not and need to be up in 3 and a half hours...

The different systems are only really compatible at the most basic level. If I were you, I'd use the other systems only as a basis for conversion and inspiration for whatever you're wanting to do.

Always be in the mindset that whatever you use, it'll need tweaks. This is of particular relevance when it comes to characters and character creation, since there are official rules for that; for example, a Rank 1 Rogue Trader character is supposed to be equal to a 5000xp Dark Heresy character - but that's just.. so not true. You'll end with vastly different characters.

Ganelon said:

Pretty **** close and improved with each iteration (IMO). Check out the link in my signature for a comparison of the combat rule changes between the various game lines.

Thanks for the replies guys - much appreciated.

Extra thanks for Black_Kestrel for the link.

Gan