The questions I have are (oh I wish I was a chemist), why was the Titanium and magnalium tube so much more powerful and longerlasting than the aluminium one, and in the same instance why was the one that was strontium and antimony so much weaker, but twice as long.... I found it VERY interesting and informative, but now need to know the why's...
Well it isn't rocket science - oh, wait a minute....
So, the one that was weaker took twice as long. That means it burned at half the speed, producing only half the gas per second, which accounts for the weakness. The actual question, then, is why it burned slower, not why it was weaker. And to answer that I would suspect it has something to do with the oxidizer (strontium nitrate), which is hygroscopic, and the weather. The fuel also plays a part because, other things being equal, the gerb that burns hottest will be most powerful, and your finely divided titanium and magnalium will be a lot more reactive and hotter burning than some oily aluminium turnings that probably wouldn't pass a 10 mesh sieve.
