Thread: Case head separation imminent

I had twice fired hornady brass doing this to prob 5 out of 10 casings

Originally Posted by Padox

I had twice fired hornady brass doing this to prob 5 out of 10 casings

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

Was only made worse by using magnum primers standard primers good as magnums were causing them to split

Originally Posted by Padox

Was only made worse by using magnum primers standard primers good as magnums were causing them to split

Greetings @Padox,
Magnum primers have negligible effect on the cause of head separations. In a chamber that is too long for the cartridge (or a cartridge that is too short for the chamber) the case starts to stretch at a pressure of less than 40,000 PSI. The front half of the case is gripping the chamber walls and the solid head of the case is forced back against the bolt face. This results in a groove as shown in the OP. Most cartridges operate at a maximum pressure of between 55,000 and 65,000 PSI so the small amount of additional pressure from a magnum primer has no effect on head separation. 40,000 PSI is around or below start loads for most high pressure cartridges.
Regards Grandpamac.

This is in a 270 running 52gr of win 760 so 1.5gr below max book load and it only seems to happen in the 1s I used magnum primers in the rest are fine so far I've had 2 sleeve in the chamber and prob 10 actually split the casing around that Grove line I was contemplating weather it was my load or my rifle I have been using the same load for prob the best part of 10yrs and the 1st time iv ever had an issue with it and the only dif was I had to use cci mag primers cos I couldn't get any Winchester large rifle

Originally Posted by Padox

This is in a 270 running 52gr of win 760 so 1.5gr below max book load and it only seems to happen in the 1s I used magnum primers in the rest are fine so far I've had 2 sleeve in the chamber and prob 10 actually split the casing around that Grove line I was contemplating weather it was my load or my rifle I have been using the same load for prob the best part of 10yrs and the 1st time iv ever had an issue with it and the only dif was I had to use cci mag primers cos I couldn't get any Winchester large rifle

The cases must be getting sized too much, and maybe the batch that got the mag primers were previously fired more than the std primer batch or just got sized more ?. I have a Rem 270 and a BSA CF2 270 no probs with these but a BSA Hunter ( been rebarreled to 270 from 7x57)I have wont fire factory ammo because the chamber is too long and the cases are pushed too far away from and by the firing pin. Maybe the chamber on that rifle is slightly longer than standard ? I have had separation with a 2506 AI when I first got it, caused by a die set that shortened the cases too much on a full length size.

Originally Posted by Moa Hunter

The cases must be getting sized too much, and maybe the batch that got the mag primers were previously fired more than the std primer batch or just got sized more ?. I have a Rem 270 and a BSA CF2 270 no probs with these but a BSA Hunter ( been rebarreled to 270 from 7x57)I have wont fire factory ammo because the chamber is too long and the cases are pushed too far away from and by the firing pin. Maybe the chamber on that rifle is slightly longer than standard ? I have had separation with a 2506 AI when I first got it, caused by a die set that shortened the cases too much on a full length size.

All casings are 3rd firing fired 1ce as factory ammo reloaded 1ce reloaded again and separating all been batch loaded 100 half had win primers other half had cci mag rifle is a Rem 700

Originally Posted by Padox

This is in a 270 running 52gr of win 760 so 1.5gr below max book load and it only seems to happen in the 1s I used magnum primers in the rest are fine so far I've had 2 sleeve in the chamber and prob 10 actually split the casing around that Grove line I was contemplating weather it was my load or my rifle I have been using the same load for prob the best part of 10yrs and the 1st time iv ever had an issue with it and the only dif was I had to use cci mag primers cos I couldn't get any Winchester large rifle

Greetings again,
From your description I assume that you are using 130 grain cup and core projectiles. Looking at the data your pressure is around 48,000 CUP. This is well above the 40,000 CUP or PSI (the two are very similar at this level) by which the case stretching and head separation occurs. Ball powders like 760 are harder to light than the extruded stick powders and the WLR primer is formulated for it. Consequently the WLR primer is often considered to be hotter than other non magnum primers. My old Speer No 9 manual from the 1970's lists the CCI 250 Magnum for use with their 130 grain projectile and 760 in the .270. I don't doubt the experience you have had but find it hard to blame the primer for case separations. That said if you can get the Winchester WLR primers they are likely to be the best match for 760 in your loads.
Regards Grandpamac.

Originally Posted by Padox

This is in a 270 running 52gr of win 760 so 1.5gr below max book load and it only seems to happen in the 1s I used magnum primers in the rest are fine so far I've had 2 sleeve in the chamber and prob 10 actually split the casing around that Grove line I was contemplating weather it was my load or my rifle I have been using the same load for prob the best part of 10yrs and the 1st time iv ever had an issue with it and the only dif was I had to use cci mag primers cos I couldn't get any Winchester large rifle

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

Originally Posted by veitnamcam

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

I understand what causes it vc I just can't understand y 1 lot would do it and the other half of the batch hasn'tso 1s on the left have separated 1s on right were pulled but same batch