Flat primer question...

[Jethro]

I just started loading for a new cartridge. This one is starting out with a bit of a problem.
I ordered new nosler brass for it. They are blems, but supposedly cosmetic.
I ran them through a full length sizer die, and started loading my ladder.
When I started shooting them, I was immediately getting "somewhat flattened" primers...even from the starting load. I fired two more rounds with same results....no better, no worse.
I stopped my ladder to investigate. I was nowhere near max. Had only gone up one grain in three round. Upon investigation, I found that all my brass was .010" under what my 3 fired rounds were. Headspace...base to shoulder. I used a comparitor for this. I re-prepped those three pieces with only neck sizing. Loaded to where I had gotten in the ladder. All three the same...and fired them. The primers now look normal.
Do I go ahead and load the brass thats "to short", and just go on with life excepting the flat primers, or what? Im sure the next loading will be fine, but what do I do now? Mup has been helping me with this, but I dont want to put it all on him. Is it safe to use these, even though the headspace is off and is flattening the primers....until fire formed?
Pics are the same 3 pieces of brass. One pic is what its doing with the short brass. The other is how they do after fire forming.
And this is a brand new rifle...its the brass thats off.

IMG_20220411_102043__01.jpg

IMG_20220413_122142__01.jpg

[JCodd]

Those primers don’t look flat. You can still see a radius on them. Not sure what the headspace measurement is, but .010 in virgin brass isn’t a concern. Thinking my 300 wm is closer to .020. If you feel uncomfortable load them on the lighter, fireform them all and start your ladder testing.

[Jethro]

Those primers don’t look flat. You can still see a radius on them. Not sure what the headspace measurement is, but .010 in virgin brass isn’t a concern. Thinking my 300 wm is closer to .020. If you feel uncomfortable load them on the lighter, fireform them all and start your ladder testing.

I agree, they aren't "flat" flat, but you can see the difference. I assume that once I get into pressure, the difference will be more severe. The first pic is 3 different charge weights. Should I expect this to continue as is, or get worse as I go up. Ive got about 4 more grains to go before max?

[JCodd]

I’m not seeing an issue with the primers and would continue on. Ejector marks and swipes along with a heavy bolt are much more concerning. I can remember the days when the little ridge around the firing pin detent was a big deal until I learn most of the holes are oversized and primers like to flow. They’re the weakest link at this point and I don’t think there’s an issue.

[Wiley]

They aren't flat to the point of cratering around the firing pin indention and that's where I get concerned. A few years ago I had one load that flattened and cratered but man was it accurate. I quit loading it though and don't even remember what caliber it was.

[Huntaholic]

None of those would concern me in the least. I don't see any extractor marks, or craters, so PERSONALLY I would load them and keep going with my tests.