kreynolds--
While I don't agree with the needlessly confrontational tone this discussion has taken (not particularly your fualt or psifon's, just a rather gradual progression), I don't recall a rule anywhere stating that the impact can't BOTH trigger the spell and still cause the natural physical breakage of the item. If I am wrong about this, point the rule out to me and I will happily concede it. Otherwise, I would have to rule in my game (not a house rule, but an interpretation of what is already there) that the impact would cause both the spell to trigger and the breakage of the glass container that was specifically made for this purpose.
Now, if there is still a problem with this, and you don't buy that the container would break because of the spell, then would there be a problem with shrinking just the liquid alchemists fire, putting it into a small glass container created to break using the rules for grenades, and then using that? The container would break, the liquid would hit a solid surface, it would expand, and cause damage. In fact, if it didn't expand instantly but expanded slowly, wouldn't it cause more damage as it slowly came into contact with more of the victim?
Additionally, if the above doesn't work (for some reason) then why ciouldn't you just do what was mentioned before, and turn the liquid into the clothlike substance, then attach the cloth to the tip of the bolt?
There seems to be a lot of ways to skin this particular cat, and many of them seem to have very few, if any, problems under the core rules without resorting to house rules. So what's the problem here regarding the delivery of the alchemists fire using a shrink item spell and a crossbow? It seems to be proven that there are ways to make it work, even if psifon's original plan is rejected.
As to your point about the amount of damage being a house rule, I might to agree with you there. However, the question is, under the current rules, without using house rules, what DOES happen when someone gets doused with 2 gallons of alchemist's fire? It has to be different than getting doused with 1 pint of the stuff. Does it cause the same amount of damage, but have a larger splash area? Or does it indeed count as a eapon of larger size, and as such follow the exact progression psifon listed, making it not a house rule after all, but the exact interpretation required? I'm not trying to imply anything here, just asking what your ruling would be, by the core rules, leaving the discussion of the shrink item spell aside, of someone getting hit with 2 gallons of alchemists fire. There HAS to be a way to interpret this, since it is a very real possibility. I have a friend who has his keep trapped with this stuff--projectors that spit a large amount of alchemists fire out onto potential wall scalers, and a vat of the stuff ready to drop on unwelcome visitors coming through the barbican. What are the rules for this kind of exposure? If there are none, then I would have to say that coming up with a system for this kind of thing, using the core rules closest in spirit to the rules you are trying to interpret, does not the creation of house rules, but the interpretation of rules that are already there.
I'm not trying to offend anyone, particularly not you, kreynolds, because you have been making some very good points, but I'm also hearing a lot of you saying a lot of "that's a house rule" when it seems more like someone trying to interpret the existing rules, and a few instances of "that's what the rules say" when I'm not aware of any rules that say that. It doesn't mean those rules aren't there, and if they are, please point them out to me and I'll concede those points to you. But if there are no rules saying, for instance, that when an action triggers a magical property it cancells out all other physical damage or other physical effects that would normally happen as a result of that action, then some of the points you have made above would seem to be invalidated.