The Senate version of the bill had so many "poison pill" expansions of Federal gun-control laws, including an AWB extension, that it needed to die. The House passed a clean version of the bill, and hopefully there were enough Republican gains in the Senate to pass a clean version next year.
As for Allen's stance on the AWB, he was initally against it, flipped his position in October, 2000 just before he was elected, then flipped back this year by voting against it when it was approved as an amendment to the lawsuit pre-emption bill. I suspect he changed his stance because 1) Governor Mark Warner will challenge Allen for his seat in 2006, 2) Warner has done nothing to anger gun owners and in fact has signed into law every pro-gun bill passed by our General Assembly, and 3) Allen is a savvy enough politician to realize that angering one of the GOP's core constituencies in a "red" state is not the way to get re-elected.
Senator Warner, OTOH, is a disappintment.
Warner will not run for the US Senate against George Allen. He can't win. He may very well run for POTUS. We shall see.