The crime decrease was extensively discussed here: https://news.ycombinator.com/item?id=5674263
The most visible and perhaps biggest of the relaxations of gun control is the nationwide sweep of shall issue concealed carry regimes, now around 42 states and 2/3rds of the population, see this for more details: http://en.wikipedia.org/wiki/Concealed_carry_in_the_United_S...; the recovery through political means of the fundimental right to bear arms is no small thing. You may laugh about my "filthy obsession", but the facts on the ground are that every time I exit my residence, I can carry a concealed handgun, and almost every time I do. That wasn't true here in my home state before 2004.
As for a study, not only are there plenty, but since you've made up your mind, for what purposes do you desire one?