So, my only experience with this slide modification is on the P365 X-Macro and I do not shoot the P320 or P365 platforms all that well. However, I was all over the place with that gun. After swapping the slide and barrel to a P365 XL, the groups tightened up a bit. I can’t say that there was a noticeable change in recoil or muzzle flip with the expansion chamber.
This modification is being brought over to other product lines such as P320 and P226 X-Five. Now, it may be that the expansion chamber’s performance is variable depending on a variety of factors ranging from barrel length to bullet velocity/pressure. That is to say, it’s very possible the expansion chambers performance is best in longer barreled guns.
Still, from a competitive perspective, I’m not seeing this as an advantage since the expansion chamber is considered to be a comp that moves the gun into open division. That begs the question is the expansion chamber beneficial for defensive use?