Felt this on my face….

56.7 is on the top end, no question. I'd switch to Fed215/215M or CCI250 if you're going to run that heavy a charge. Some primers can't take that kind of pressure.

In all of my testing with 140's, I hit heavy bolt lift right at 57gr of H4831SC at a velocity around 3050fps. So you're pushing it. I'd back that off for certain.


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Most likely, a bad primer wall. Through the decades, I and friends have seen a few of these on various loads and cartridges, and if memory serves, they were always related to a weak primer that pin holed. Depending on year/s and lot of mfg, some brands are more prone to this.
 
Was it a win primer? They had some bad primers a few years ago-- if you pop the primer out and see if it's a pin hole in the primer or between primer and pocket wall.

Probably too hot too.
 
Hodgdon doesn't show a 140 grain load with H4831SC, its H1000, US 869 or Retumbo. Berger doesn't show 6.5PRC load data at all so nothing on their website with the 140 with H4831SC either. I attached load data from Hornady that shows 143ELDX max load with IMR4831 at 52.7 gr which is slightly faster than H4831SC. I would contact Berger to validate your load data since dropping one grain may still not be where you need to be with H4831SC and this bullet. Good luck!
 

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Hodgdon doesn't show a 140 grain load with H4831SC, its H1000, US 869 or Retumbo. Berger doesn't show 6.5PRC load data at all so nothing on their website with the 140 with H4831SC either. I attached load data from Hornady that shows 143ELDX max load with IMR4831 at 52.7 gr which is slightly faster than H4831SC. I would contact Berger to validate your load data since dropping one grain may still not be where you need to be with H4831SC and this bullet. Good luck!
Here is the data that I got from Berger a couple months ago...
140gr VLD Hunting.png
 
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