Why am i blowing primers ( Rem 7 1/2 br) ONLY

[Webster]

The firing pin hits the primer and the excessive head clearance allows the primer to move back over the firing pin and it acts like a cookie cutter and punches the center out of the primer. This is why military primers are crimped, it keeps the primer from moving to the rear.

 

[Webster]

I would think all factory loads have a lot of headspace without this problem? Can someone measure the head space (case shoulder to chambr shoulder) on some factory rounds and put them on the website. I have never seen actual numbers.

 

[Doom]

The 7-1/2 is a magnum primer mix and hotter than all other SRP’s. Assuming a carbon ring isn’t the problem, you need to back off the powder charge.

 

[Twdmar]

The 7-1/2 is a magnum primer mix and hotter than all other SRP’s. Assuming a carbon ring isn’t the problem, you need to back off the powder charge.

German Salazar did a test of primers for Riflemans Journal site many years ago. He made a fixture to fire the primers and had essentially a ruler that measured the flame produced by the primers. He captured the flame with a high speed camera. I don't remember if he tested them for pressure when he had the strain gage testing pressures.
His results showed a significantly larger flame with rem 7 1/2s compared to most other primers and in his opinion, they would produce greater pressure. Hence the 7 1/2 being thought of as a sort of magnum primer.
As to the remington cups being soft and that being a problem, I don't see it. Service rifle shooters like them because the cups are hard and don't suffer slam fires like some other primers.