Oh, I tend to do my best work with guns meant for self-defense. Sigs are my favorites. I have been building some ARs lately, too. Lately, people have been asking for the easiest upgrade ever.
If you have a P365 with the 3.1" barrel, buy an X-Macro handgrip and a Radian Ramjet/Afternurner. Total install time is less than 5 mins - swap the FCU into the X-Macro, swap the barrel, dog down the afterburner to 15lbs, put the gun back together, and do a function test.
When you go fire it, you will be amazed at how much tighter your groupings are, and how much more fun the thing is to fire. Handles and fires much more like a Glock 19 than a micro sub. Add an optic or Laser/Light, and you have one heck of a carry weapon.
Given the coming tobacco apocalypse, you may need it too. Dang theives!