Inactivate a pistol question

Due to a long story of being caught up with the changing rules and transfer times I have ended up with a extra pistol which I would like to have made inactive (de-activate) for the purposes of running training drills off site. My hope is to keep it as a functioning parts pistol which would not require an ATT.

Has anyone done this? What methods did you use?

Need to take to a reputable gunsmith / verifier who can render action and firing pin inoperable, and provide paperwork for same.

You then need to file paperwork with CFC that the pistol is deactivated.