I have a 6 CM and before Lapua brass was available, I reloaded Hornady first, and then Peterson. Honestly, I had some issues with Peterson (not as many as Hornady, though). First off, I noticed that on a few casings, the primer hole was a little off center. I also had some issues with the primer pockets being too tight. I broke A LOT of depriming pins on the Peterson brass... and I mean A LOT. I've never broken a pin on any other case. I finally went to a handheld depriming tool with a hardened steel pin. I actually use this for everything now, so it worked out, but still...
Anyway, using Peterson, I was fighting to get to 3/4 MOA groups at 100 yards in my factory Bergara HMR Pro. At 300, I was lucky to get 1 MOA - though, some of this was due to my failing eyesight impacting me at this range - something I've since fixed with prescription shooting glasses. The first time I went to the range with new Lapua brass, the image below was my best 5-shot group at 100 yards - all were in the 1/2 MOA ballpark. I was shocked at the consistency difference between the brass. Again, this was out of the box new Lapua brass, and it performed better than reloaded, properly sized, prepped Peterson. All I had done to the Lapua in this pic was deburr the primer hole and chamfer the neck before loading it.
I'm going to the 100 yard range tomorrow to get my new 300 PRC barrel broken in. The friend I'm going with loves my Bergara, so I'm taking it along. I've got 50 rounds of Peterson brass loaded, and maybe 30 Lapua. The Peterson has been filtered based on primer hole consistency, so this should be more consistent than out-of-the-box casings. I'll let my friend fire 30 or so of the Peterson, then I'll do a side by side comparison (same day, same rifle, same shooter) of Peterson vs. Lapua and post the results.
EDIT: I have not fired filtered/sorted Peterson brass before, so I am interested in seeing the results.