He wasn't prepared for it. "Prepared for it" means "I cast a veil making me appear 2 feet to the left so aimed sniper shots will miss". It may also mean "I go shopping under a 'don't notice me' veil/potion cause there's a war on and I want to live".
One of the things Harry doesn't really do is prepare - he has the wrong temperament for it. Even the bigger wards for his house only come because some zombies almost ate him when the old wards he never bothered to beef up failed.
Acutally, if I recall correctly, at that point he HAD beefed up his wards. The problem wasn't they weren't strong enough, it was in the way they were erected. A vamp comes up to his door, he gets vaporized. This stops most intruders. However, (potential spoiler from Dead Beat)
he had never really thought that a Necromancer would throw wave after wave of zombies, to slowly wear away the power of his wards.
It was a weakness in design.
Now, back to the topic at hand, I was wondering how exactly you would determine the AP value of a weapon, if you were to go about with that particular house rule. I noticed you mentioned the .50 cal as weapon: 4, AP(3). Was that just a random number off your head, or was it basically saying that you think a weapon's AP value, if it has one, should be equal to 1 less then the weapons value?
Second, I want to say, although I couldn't actually say for certain, or cite a page, that the example of an Armor Piercing Aspect for ammunition was mentioned at one point in the book. I think it was also shortly followed up by another example of a special ammunition, who's tagging of an Aspect could allow you to satisfy the catch for someones Toughness. But it never went into detail of what exactly an Armor Piercing Aspect would do.
Maybe you can tag it, to completely bypass an Armor's Armor Value? But at that point, it seems to just kinda get silly.... Maybe certain levels of armor, give or take, from 1-2 would classify as having the aspect of "Lightly Armored" or something along those lines. Smaller caliber firearms with AP rounds could have an Aspect of "Light Armor Piercing", which can be tagged to negate the effects of Lighter Armors. Then armors from 3-4, professional military gear and full Riot Armor, could have a heavier form of the "Armored" Aspect, requiring a heavier form of AP rounds, like the .50 caliber to field a heavier "Armor Piercing" aspect. But once you go into all those, you kinda get outa the simplicity of the FATE system, and into more rulsy guidelines you need to start following.
Anyway, I was just wanting to know exactly how you would go about doing putting together something like this, as it would be very helpful for my upcoming campaign.
