Don't take this as official word from HK or anything. But in my own experience the stepped chamber is fantastic for both accuracy and reliability. Since I started shooting VP9's, I've stopped case gauging my ammo, even for major matches. There just isn't a point in the wasted time for me anymore. With the stepped chamber, they will feed even significantly out of spec reloads, and each of them is capable of sub 2" groups at 25 yards when I don't suck.