My SOP back when ammo was plentiful was I would run 500 rounds of FMJ and a 50 round box of the carry ammo I was going to use. I have not transitioned to a new handgun except for one recently and that is a P365XL. I have decided to start carrying it, but have only ran 200 FMJ rounds through it and 20 rounds of defensive ammo.
I do not completely trust any gun right out of the box. I do tend to trust some more than others. For example I would feel more comfortable running maybe 50 rounds through a Glock / M&P / CZ P07/P09 and then putting it into service, however with a 1911, I would need more rounds than that to have full trust.
With a revolver, I am good to go with running a few cylinders thorugh it. In the end, I would never take a gun out of the box new/used and put it right into service.