Early or recent VP9? I believe the current production VP9 and VP9T have VP40 springs in them.Just shot a new out of the box VP9 Tactical with AAC TiRant 9. Shot well suppressed, with only one oddity - slide didn't stay locked back after the last round when suppressed (but did stay back when not suppressed).
This suggests to me that the side isn't getting all the way back when suppressed, which means that I'm close to a FTF. Maybe just need to break in the recoil spring. Watching this.