Not on the sides, only at the end, but only a few... this was the worst one.
My new MPA (in 6.5CM) rifle does the same, leaves the chamfered edge of the neck mangled. Need to press the neck down on sand paper and rotate the case to remove it. Happens on 30% of the cases. Cases are getting shorter as a result, not growing... Don’t like this behavior either.
The MPA has a “match chamber” cut into the barrel, which is on the tight side. Probably not your standard SAAMI chamber. Shorter freebore (a 140 ELD-M factory round is supposedly ending up with 5 thou jump), and tighter than normal necks. My Alpha brass was around 15 thou neck thickness and the fired brass just barely allowed a bullet to fall into the case. Some resistance there, so i turned them down to 13.2 thou. [You will need to measure your cases, this could have contributed. Your ideal neck thickness will likely be a little different from mine.
I loaded a new batch of 140 Berger Hybrids yesterday at 0.3 grain less than before (H4350) and the damage to the necks went away. Bolt also opened real easy.
I have tried factory 140 gn ammo (Berger factory 140 Match ammo, which uses the Berger Hybrid bullet in Lapua brass), and this batch ran real fast (2820 to 2840 fps), and cause a fairly stiff bolt lift. It also pierced three primers, and had very bad cratered primers. All signs of high pressure. [Of course: Small rifle primer in the Lapua brass, and a large firing pin combo might not be best.]. Hornady 140 ELD match ammo worked well with no issues, shot 0.45” average group size, best was 0.3”.
Gun was apparently chambered for factory 140 ELD-M match ammo, and that worked well for me. Try that.
Also, if the bullets are loaded long in this factory ammo, or if they are heavier than 140, you might be getting a jammed bullet in this particular rifle (will not be the case in SAAMI specced chambers), and that can severely spike your pressure. Try different ammo. But please stop shooting this ammo, likely you are way over the pressure rating. The manual basically says do not shoot anything heavier than 140 grain bullets.
