I recently purchased an aftermarket barrel for my P320 x5. I sent the manufacturer a dummy round to that they could Ream the chamber to fit my ammo. This is my carry optics gun and when I went to zero it in, I was getting a 6-7” group at 15 yards from a rest. I put the OEM barrel back in, and the group size went back to 1-2”.
Speaking to the manufacturer, they had me check the fit, and everything looked good. However one thing I did notice is, they must have reamed it slightly too short. My ammo ranges from 1.130-1.135 and the 1.135 rounds don’t pass the plunk test. The ammo is slightly too long, maybe .002-.003, could this be the cause of the blown out groups?
I’ll add that I have another barrel from the same manufacturer on my 2nd x5, and it groups beautifully with the same ammo.