Depends on how good a shot you are.
I don't think more than 5 or 10 targets will present before the rest determine that the grass is greener a few miles away.
There are 4 things that are useless to you: altitude above you, runway behind you, fuel still back at the pump, and ammo you didn’t buy.
It depends on how many bodies you want around afterwards. The problem is that you would want to keep them well OFF your property line. At the later trial, what will you tell the jury, as your justification for shooting somebody a hundred yards away from your house?
During the Rodney King riots, the Korean store owners would fire at the ground near the feet of the rioters to convince them to back off, and to indicate the red line. Doing it that way, maybe one shot per minute, results in the expenditure of 600 rounds over the course of the night.
Then again, if it turns into general war, then the concept of trials go out the window. If there are thousands of dead, and thousands of shooters, there will be no trials. What there will in place of trials, of course, will be determined by whether Obama is still in charge, and who is willing to follow his orders.
As for me, I choose to have a lot of ammo available. A friend of mine once told me "You're going to run out of luck before you run out of ammo". That's how I like it.