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Good reply above from Grandpamac.

Check the rest of your cases, if they are relatively clean on the outside you can usually see the line but definitely would be worth checking them all with a...

Grandpa Mac has well covered ( perhaps more easily understood hopefully)again what I was trying to explain in post 1 and 2.

If your rifle has large chamber dimensions and you shoot factory ammo...

How do you set up your dies?
I'm picking your rifle might have a chamber at the big end of Saami spec and FL dies set up to instructions will cause this fairly quickly.

Measure those fired cases vs the ones you pulled as per Cigars picture above to a mid point on the shoulder.
If you don't have a ogive measuring set or something you could use a short bit of tube...

Go back and read post no 1 and 2 again.
Primers are not going to cause case head separation.....even overloads are unlikely to.
What causes it is explained in post 1 and how to avoid it in post 2

That is how it is measured yes, but the headspace is the amount of clearance between the cartridge and chamber dimensions.

You must have had very large headspace and or chamber dimensions to get that on only two firings.

Unsure... probably at least 10 times and in 4 different rifles.
It's my "Beater" brass I don't care if I lose so use for bush loads and start of load developments so has had a hard time in more than...

A stuck case and possibly a bit of gas back in your face

Most full length Sizing die instructions tell you to wind the die down to the shell holder and then + another 1/4 or 1/2 turn.
This will produce normally brass that should chamber in most rifles of...

Case head separation,what to look for and how to avoid it comes up fairly often on here so when prepping some of my "beater brass" today I found one and thought I would section it to show what to...