I wouldn't loan a gun to my best friend.
Suppose it gets stolen?
I did this once. To my (now former) best friend. And the gun did get stolen. It was recovered, but because of the BS story he supposedly told the cops (different from the one he told me), and a couple of other things, the gun was held as evidence, and the charged individual never showed up for their hearing, so the gun is held until that person gets charged. Odds are real strong I'll never see that gun again.
I had known the guy over 20 years, and he still did me dirt. I no longer even consider loaning a gun to anyone, (except my children, and they have their own) or my wife.