Designing Sound has a detailed feature on planning and carrying out a gun recording session, featuring sound designer Chuck Russom:
In this article I’m going to share the approach I have used to plan and conduct gun sessions. I rely on professional, private party resources to provide weapons and locations. While others may have had success with police or military, I prefer working with the private sector as I can ensure that I can get the weapons I need, work in the locations that I choose, and work under my timeline. To get the results that I am after, I need to control as much of the process as possible. It takes a lot of effort to record guns and I want to be sure the effort pays off.
Read the full feature on recording guns here.