Head separation and dimpled case body
- Thread starter Area Man
- Start date
BoydAllen
Gold $$ Contributor
Because of the issue of firing pin tip fit in the hole in the bolt face, and the shape of the edge of the hole, I don't use cratering as an indicator of pressure, preferring to look at other things, the corners of the primer, the presence of a bright mark where the ejector hole is in the bolt face (When you get this you definitely are too hot.) and bolt lift. Warmer loads will also have the face of the primer, not counting any crater, flush with the case head, whereas lower pressure loads will leave the primer a thousandth or two proud of the head. This can be observed by holding a case between the jaws of a caliper, and up to a light source. Another cause of cratering can be the shape of the firing pin tip. If the radius extends too far down the side it can leave a small area that is not filled. A long time ago, someone told me that a proper tip shape consists of two different radii, a larger one in the center, and smaller one at the edges, not a hemisphere. I have had rifles that cratered every primer, but never pierced or blanked one, including loads that were quite warm. As long as that is the case, I don't feel the need to fix anything.
The cases he was showing was clean not the one that showed the blowbuy dimple. LarryArea Man said:
We don't have a commutation problem. We have a problem of not reading the whole article before engaging my mouth. LarryLHSmith said:savagedasher said:
What we have here is a failure to communicate :....I can clearly see carbon on the neck/ shoulder junction, I vote for blow-by from the case head separation.
I noticed cratering with mild loads on a new Rem 700 back in 2009 and did some research on it. I found an article (which I cannot find again for the life of me) that explained how Remington deliberately chamfered the firing pin hole to cause it. I did find the following, which pretty much says what the article had said.
Direct from Remington:
Discussion Thread
Response Via Email (Danny) 08/30/2012 01:00 PM
The cratering you are seeing is normal on the gun manufactured between 2008 and 2010. We began putting a bevel on the face of the firing pin hole in order to allow the primer cup to flow back and thicken the primer at the most likely point of failure during the firing pin strike. This was to reduce the likelihood of a pierced primer and greatly reduce the risk of injury to the shooter overall.
Customer By Email (hugo) 08/30/2012 12:55 PM
Direct from Remington:
Discussion Thread
Response Via Email (Danny) 08/30/2012 01:00 PM
The cratering you are seeing is normal on the gun manufactured between 2008 and 2010. We began putting a bevel on the face of the firing pin hole in order to allow the primer cup to flow back and thicken the primer at the most likely point of failure during the firing pin strike. This was to reduce the likelihood of a pierced primer and greatly reduce the risk of injury to the shooter overall.
Customer By Email (hugo) 08/30/2012 12:55 PM
CatShooter
LRGoodger said:
This is, of course, pure bull-scatology.
Primers that flow back into a bevel, do not get thicker, they get thinner.
BoydAllen
Gold $$ Contributor
Craters and pressure:
MANY year back, I had an '03 Springfield, with a double heat treat receiver, and an 03a3 bolt, that had been fitted with the strongest spring that strong hands could manage to assemble on the two piece striker. The hole in the bolt face was an excellent fit for the firing pin tip, and the edges of the hole were quite square to the bore. One night, when I had been loading well after I should have hung it up and gone to bed, I overloaded some rounds with AA2520 to the extent that when I fired the first one, the primer pocket was expanded so that it looked like it might take a shotgun primer, and the primer literally fell out of it when the action was opened, and the case was extracted. (I had removed the ejector because at that point I was doing all of my shooting single shot, from the bench.) The point of this tale is that that primer did not have a crater...none, zip, nada, and nothing about the rifle or shooter was damaged in any way, except for that one case. Of course I stopped shooting right there and when I got home I pulled all the bullets, and weighed my charges to exactly what I had done. The firing pin tip was the standard diameter, similar to Remington 700s use, and I have no idea what the weight of the spring was, except that it was very stout.
MANY year back, I had an '03 Springfield, with a double heat treat receiver, and an 03a3 bolt, that had been fitted with the strongest spring that strong hands could manage to assemble on the two piece striker. The hole in the bolt face was an excellent fit for the firing pin tip, and the edges of the hole were quite square to the bore. One night, when I had been loading well after I should have hung it up and gone to bed, I overloaded some rounds with AA2520 to the extent that when I fired the first one, the primer pocket was expanded so that it looked like it might take a shotgun primer, and the primer literally fell out of it when the action was opened, and the case was extracted. (I had removed the ejector because at that point I was doing all of my shooting single shot, from the bench.) The point of this tale is that that primer did not have a crater...none, zip, nada, and nothing about the rifle or shooter was damaged in any way, except for that one case. Of course I stopped shooting right there and when I got home I pulled all the bullets, and weighed my charges to exactly what I had done. The firing pin tip was the standard diameter, similar to Remington 700s use, and I have no idea what the weight of the spring was, except that it was very stout.
CatShooter
Area Man said:
It is done because the bolts are drilled from the rear, so the drill pops out the front of the bolt and if it isn't sharp or done in a rush, the drill leaves burrs.
It is easier to cut a bevel to remove the burrs, than clean them flush.... but I don't think they do it anymore??
What is the best process to fix the problem
What is the best process to fix the problem
Because it is NOT related to the problem. Soft rings like this are caused by the hole in the bolt being a fair bit larger than the firing pin, or the pin hole being countersunk to remove the burr from drilling - pressure caused craters look very different.
When Full length sizing make sure you're not bumping the shoulder more than 0.001"... 0.002" MAX.
You'll need a Hornady Headspace comparator or a 40 S&W empty case until you get the comparator.
Measure the case before and after sizing to make sure the shoulder is not pushed back more than 0.002"
Neck sizing will also help but neck sizing only works so many times before the brass starts to fit tightly in the chamber and needs to be FL sized.
Dusty Stevens
Shiner
Belted magnums are just a problem. No die works the shoulder and belt correctly they usually just go one or the other too much. I used to shoot tons of belted magnums but i try not to anymore theyre just a problem all around
I've had no problems with Belted magnums mainly because I set my own headspace according to the brass I'll be using. Then the first load cycle is with with bullets jammed to prevent stretching above the shoulder. Then bumping the neck 0.0005" to 0.001".
Otherwise I don't recommend more than a handful of reloads on a belted case. Weather neck sized or shoulder bumped to a minimum. And no more than 3 reloads if FL sizing with out knowing how far the shoulder was set back. Just to be on the safe side.
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