Blown primers with min starting load

How many different powders has he tried or the same-same? no change of powder?
Doesn't take me long to figger out somethings fucked up.and change something
but I never load over 5 rnds and shoot them and if they don't do good, I change.
5 rds. of each powder I load with and find the one that does the best or what loads well on the bench? or what you have a lot of.
It's not how fast you go, It's how you get there.
My first reloads were with N555 with no problems. I switched to H4350 with a higher charge than theses problem rounds but had no issues, they were just running faster than I was trying for. I reduced the powder to the charge weights in my original post and the problems began. That’s the only variable that changed. It’s counterintuitive but as I posted earlier I’m inclined to increase the charge some (obviously well below max but in the neighborhood of where I started with H4350).
 
I’ll order one today. Wouldn’t these issues also show with the factory ammo if carbon were the culprit though?
Just me....but personally fuck bronze brushes in my bores.

I use a properly sized mop, soak it in BoreTech Carbon Remover (and Eliminator may work just as well) and push it just past the end of the bore guide so that covers where the neck ends and the throat begins....and leave it there over night. Gets the carbon deposits just past the neck area out.

Yes, I know....many have used bronze brushes for decades without issue...but I don't. They are fine for shotguns
 
You can try these to confirm what your chamber actually measures , all my rifles have been on the long side of SAAMI specs . I have never seen one come up short, but you never know . It will surely let you know if the case mouth is being pinched . What is OAL of new factory brass and after being fired ?

 
Yes he said in the OP the Lapua brass is on its 5th firing. That was why I suggested donut.

I have had some resistance pushing a bullet into the case before, but it was because one side of the neck was flattened some as it ran down the inside of the action during extraction.
 
I have more powder in unopened canisters of different lots that I’ll use. I’ve only loaded with the two powders and always empty the hopper and trickler after loading. Obviously I’d like to isolate the cause, but honestly feel like I’ve checked everything I can. I’m not sure what other variables other than the particular lot of powder or the brass I used can be changed. As I said initially, it’s quite disconcerting, but I’m not sure there’s anything left to verify.
I believe it could be the powder. Yes try another lot of the 4350 and shoot those to see if there's any difference. If there isn't then get another powder, if it does change and behaves like it should then contact Hodgdon.