split cases

retiredcpo

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Any ideas on the problem we are having would be great
thompson encore in 300 win mag
Had a problem with the cases spliting off about a 1/2 in from the bottom
scratch our heads check stuff talked with thompson they looked at the barel said it had excesive head space and replaced it
we had scope problems got that worked out and started shooting again
and the case split off again check some more rounds and several had cracks in them. some shot cases shown slight signs of primers flatting out.
loading 71 gr 4831sc 190 gr bergers .005 from the lands.
the case splitting does this sound more like excesive head space or pressure problems.
second if the measurements on the loaded shell where off say .007 putting the bullet into the lands chould this cause pressure problems?
thanks
retiredcpo
 

vintec

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your reciver could be flexing, check the length of the brass before and after it is fired
 

retiredcpo

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vintec
interesting idea never thought of something like that
maybee to much recoil for a break open gun?
its a buddies gun not mine btw
 

Chas1

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Let us know what the b4 & after measurements are.
 

Moman

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The case splitting definately sounds like a headspace issue. It would be intersting to take a headspace measurement on the datum line of a new case and then compare it with a once fired. I had a Rem 700 that would stretch the shoulders .014 on fireforming but it was still able to get 5 or more reloads, depending on the brass. Good chance both these barrels were chambered with the same reamer.

The flattened primers sound more of a pressure problem. Maybe try backing the load down some or seating a little deeper. Or both.
 

retiredcpo

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its all reloads with 4 or 5 loads on the cases
We have no idea what the before measurements are
 

dud

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4 or 5 loads on 300 mag.did you check inside cases for cracks at or above belt?
 
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4 or 5 loads on 300 mag.did you check inside cases for cracks at or above belt?

I am guessing your splits are circular, and if that is the case what you are getting is cartridge case stretch. A thin white or light yellow line appearing around the cartridge case just ahead of the belt is your first indication.

To test further take a paper clip and straighten it out(leave the last loop it will act as a handle), file a point on the straightened end and then bend it to a 90 degree angle about 3/16” from the sharpened end. Insert the bent, sharpened end into the cartridge case mouth, and beginning at the web in the bottom of the cartridge case, move the pointed end slowly up the inside wall of the case. If a stretched or thinned area exists you will feel a groove on the inside wall of the case. Check every piece of brass and discard any that are suspect.

This is a headspace problem or an incorrect resizing die setup (you are bumping the shoulder back excessively and over working your brass)

Steve
 

Jamie6.5

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I have seen this problem before with belted mags.
If the cartridge "headspaced" at a datum line on the shoulder it would be a headspace problem by definition.
In the case of a belted mag however, it's not, because the "headspace" is measured at the belt.
But yet the case is stretching too far to fill the chamber at the shoulder/sidewall juncture, and at the shoulder/neck juncture.
I would call Thompson back and ask for a barrel with a shallower overall chamber depth, describing your cases.
Frequent Flyer nailed it for checking the cases, and that is definitely the correct way to go when checking for this symptom.

You can check how much stretch you are getting by measuring a new case length at the shoulder/neck or shoulder/sidewall vs a once or twice fired case.
You may even need to send some to Thompson to get them to admit what's happening.

Oh, and any cases you have fired in this "too deep" chamber will most likely no longer hold up. The stretch is already too much so you're going to have to start over with new cases.

Good luck with it.
 
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retiredcpo

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the splits are circular around the case about 1/4in above the belt.
I will suggest measuring the length of a new case before and after shooting.
 

Innovative

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retiredcpo .......

You described a very common symptom. This happens when you bump the shoulder back too far during resizing. However, Neck sizing isn't the best solution. Continue to FL resize, just do it more accurately. Check out the two items on this page



Headspace separations can be dangerous. This picture shows what your cases look like on the inside. That's where the damage begins. It can be totally avoided by "measuring" the setback of your case shoulder and setting your die height accurately - don't guess at it.

- Innovative
 

boomtube

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"..the splits are circular around the case .."

Okay. As Larry said, those are not, technically speaking, "splits", they are "head seperations" and potentially dangerous. Splits are length-wise the body or neck and are normally harmless. As Larry also point out, seperations result from stretching the cases past their ability to take it. His phoro clearly shows the web thinned at the point a seperation would occur.

Excessive case stretching is due to excessive shoulder set back when sizing OR from a "springy" action or both. You likely have both. You can minimise the excessive sizing and you should discard the cases before they seperate.

Many people speak of watching for "incepient" head seperations, the sign is a clearly seen shiney ring that forms when the brass is being stretched. Bad thing about the current craze to tumble/polish cases is that sign gets polished away before it really becomes visible.
 

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