Every dictionary I have seen says stress an in angeblich. Yet often, I hear angeblich. Does it matter? Are there rules? Or is it dialect? Similarly, ausführlich or ausführlich? One dictionary says the latter is used in Austria, yet I usually hear ausführlich anyway, which sounds more natural to me. Tatsächlich or tatsächlich? Dictionaries say both are allowed, but hauptsächlich and not hauptsächlich? Is this right?
I tried to find dictionaries with pronunciation hints on Google Books, so that we can have references here to discuss about.
Here are my findings. They all claim angeblich to be pronounced on the first syllable (which might surprise some commentors of your question):
However, I can confirm to have heard angeblich as well, and though I am not sure, I think I've already used both variants myself; probably depending on what would fit better into the rhythm and melody of the sentence.
If you check that same sources for the other references, you will see that
- three of them explicitly list both variants for ausführlich (Langenscheidt doesn't seem to have the entry in its searchable part)
- the Aussprachewörterbuch gives both variants for tatsächlich, while Oxford Duden only the one stressed on the first syllable (the other two don't have it)
- none of them seems to have hauptsächlich
My personal experience is that both variants can be heard and are "correct" for ausführlich and tatsächlich. In contrast, I feel a strong preference for hauptsächlich, but I surely wouldn't frown on hauptsächlich.
To sum it up: there are no strict rules, it is largely a matter of preference (I can't say anything about regional influences here), and distribution of preferences for the variants might not be the same for the 4 words that you asked for.
Edit: I found one more dictionary: Deutsches Aussprachewörterbuch seems to favour (if I read it correctly) angeblich and hauptsächlich and allows both variants for tatsächlich. No entry on ausführlich. So it's one more hint that there are no clear commonly accepted rules for one variant.
Go to http://www.aussprache.at and enter at »Orthographische Suche« the word whose pronunciation you want to know.
When you enter »angeblich« you will find that the six speakers (female and male voice from Austria, Germany and Switzerland) always stress the fist syllable and sometimes also the second (male voice from Austria).
In the case of »ausführlich« you can her that four speakers stress the first syllable (speakers from Austria and Switzerland) while the others stress the second (German Speakes).
So I think that in all your examples all versions that you found are correct.
But: there are cases in German where stress changes the meaning:
umfahren : to steer around (a car around an obstacle, e.g. a traffic jam)
"Wir empfehlen, den Stau weiträumig zu umfahren."
umfahren : to run over (an obstacle with a car, e.g. a sign post)
Pass auf, du wirst das Schild noch umfahren!
Edit: the fact of the matter is that in German, stress means, well, stress. One stresses the part of the word or the sentence which is most important in the current context. Depending on the word, this might the same part most of the time, but still it might be different in another sentence.
For angeblich, the base stress pattern would be angeblich, because it is derived from the noun Angabe, where An- is the most important part which distinguishes its meaning from the base form "Gabe" (gift).
However, angeblich would often be used in a sentence like
Angeblich hat er das Geld irgendwo gefunden.
where the adverb expresses a doubt in the fact, and is stressed because it is most important in the sentence. So sentence stress, which goes on the root of the word, interferes with word stress, and you hear angeblich, and the stronger the speaker feels the doubt, the more prominently they would pronounce the stress.
For your other examples, one could construct similar contexts:
Tatsächlich hat er das Geld aber gestohlen. Ich habe den tatsächlichen Vorgang ausführlich dargestellt. Ausführlicher wird man es aber in der Zeitung nachlesen können.
hauptsächlich is special in that "haupt-" means "main", and so carries its importance in its meaning already. Therefore, it would be more difficult to construct a context where haupt- is not stressed. I can't think of a good example with hauptsächlich, but one could say
Nicht alle Hauptwörter sind auch Hauptsachen.