Always been a fan of the P229 platform and I happen to have one in .40. I know how well these guns handle different calibers and I’d love to know from anyone who has actually tried adapting a .40 P229 to work with 9mm reliably.
You’re using one of the easiest platforms to get into the caliber-swap. I’ve played around with it and I have to say, the .40-to-9mm setup exceeded my expectations. The frame and slide are really sturdy so the gun hardly feels the lighter 9mm recoil. Tip is to use a good conversion barrel and authentic 9mm mags.