https://youtu.be/08crkU999Fs

In this ZBrush Summit presentation, Mike Climer gives an overview of ZBrush and techniques used that worked on designing the weapons for Destiny 2.

Tips include:

https://youtu.be/RM4ctbQq_g0

In this FlippedNormals presentation, Henning and Morten go over how to create a rifled barrel for a firearm in ZBrush.