I have attached a picture of two brass recently fired from my 7mm Dakota. The one on the left with extremely flattened primer was a new piece of brass loaded the exact same as the brass on the right which had been fired for the third time and only neck sized. The only difference between the two loads was the new brass head space was 2.062 and the neck sized brass was 2.079. Should I have two back the charge off on forming new brass as the excess head space could cause excessive pressures???
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Flattened primers?
- Thread starter snojnke
- Start date
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I believe the cartridge was able to move forward with the firing pin strike. When the pressure began to build the primer had enough space to be pushed partway out of the primer pocket. As the pressure continued to build the brass moved rearward mashing the primer into the bolt face. The excessive headspace caused this issue not excessive pressure. If you pop out a fired primer you will see a mushroom shaped head on the primer.
I hate to say this but you are going to have to make a false shoulder on the neck or seat a bullet out so it touches the lands and fireform these short cases. It is hard on the brass to stretch in the manner where it has room to move and could cause damage is where the web meets the case body.
Somehow your rifle was machined with excessive headspace or the virgin brass was made too short.
If this is a recent build you might consider talking to the builder and have the headspace reduced.
I hate to say this but you are going to have to make a false shoulder on the neck or seat a bullet out so it touches the lands and fireform these short cases. It is hard on the brass to stretch in the manner where it has room to move and could cause damage is where the web meets the case body.
Somehow your rifle was machined with excessive headspace or the virgin brass was made too short.
If this is a recent build you might consider talking to the builder and have the headspace reduced.
Your measurements indicate you have a generous chamber in your gun.
Neck sizing will get you a better fit and you might even see better accuracy with neck sized loads.
At some point you will have to bump the shoulder back. Adjust your FL die to give you minimum shoulder set-back (~.002") to extend the life of the brass.
I don't think you have to reduce your load.
I had a similar situation with my Ruger #1V 25-06, generous chamber. I ended up buying a body die to better control shoulder bump.
Neck sizing will get you a better fit and you might even see better accuracy with neck sized loads.
At some point you will have to bump the shoulder back. Adjust your FL die to give you minimum shoulder set-back (~.002") to extend the life of the brass.
I don't think you have to reduce your load.
I had a similar situation with my Ruger #1V 25-06, generous chamber. I ended up buying a body die to better control shoulder bump.
So the only thing to worry about immediately will be shortened brass life, no other concerns? How do you make a false shoulder. I try to neck size mostly but after a few firings I start to get a stiff bolt lift and end up FL sizing to set shoulder back. Thanks for the replies.
varmintH8R
Well-Known Member
Just my opinion, but I would not be comfortable firing brass with 17thou excess headspace. Even the possibility of a major issue (a-la case head separation) is enough to make me re-evaluate. That 17 thou has to come from somewhere.
While I agree you can most likely fireform using a false shoulder, this is a band-aid only - you still have a long chamber or short brass. I don't like "special case" guns. When only the operator knows how to run it safely, the possibility exists of issues in the future as it gets passed down, sold, etc.....
I would try to get some measurements from other virgin brass to see which of the above it is. If it is a brass issue, I'd see if the manufacturer would replace it. If a chamber issue, I'd have it fixed.
My 2C only.
Gunpoor
Well-Known Member
snojnke I had a custom put together some years ago that had a generous chamber similar to the rifle you describe, and I neck sized the brass and when the bolt lift became stiff I would use a FL sizer and set the shoulder back just enough to make them work. I then had to use the neck sizing die to finish them. I don't think this is detrimental to the life of the brass as long as it isn't over worked, such as complete FL sizing would.
The only supplier of 7mm Dakota brass is Dakota themselves, I'm not sure who is manufacturing it for them. At one time it was Norma not sure now though. I have ordered several batches and the have all been consistent at 2.062. I obviously have a generous chamber just don't want anything bad to happen.;
g0rd0
Well-Known Member
I have a 7mm rm like Gunpour. It has a generous chamber so I neck sise then fl sise when the bolt stats to close stiffly.
But, if you are not having those problems with all of your brass sort them into good primer and flattened primer piles. Then trim all to the same length and weight them, you may just have a batch of brass with thicker walls than the rest
But, if you are not having those problems with all of your brass sort them into good primer and flattened primer piles. Then trim all to the same length and weight them, you may just have a batch of brass with thicker walls than the rest
I should have asked this earlier. Did your once fired cases exibit flattened primers too? Or did you acquire them already fired?
I encountered a 300 win that had a great deal of headspace. Didn't see any symptoms because the belt kept the case in place during firing allowing the shoulder to move forward. Never knew till I tried to fit some of the sized cases into a different 300 win mag.
To make a false shoulder you need a larger sizer ball to expand the neck of the case. You would use a 308 sizer ball. After the entire neck has been expanded run the case back into your 7mm Dakota die reducing some of the neck diameter back to 7mm to a point where the bolt could be closed but with some resistance. The false shoulder keeps the case head against the bolt face and will allow the case to stretch and fill up the shape of the larger chamber.
It would be interesting to fireform one case then section it to study the area just in front of the web to see if it was stretched to a narrower dimension. If you found that to be the situation, your chamber is too long to use safely.
You could section a fired case and look at the area in front in of the web as well.
Probably the best idea is to have a gunsmith reduce the headspace of the rifle. It isn't that hard and doesn't require a reamer.
Let us know what you end up doing.
Ross
I encountered a 300 win that had a great deal of headspace. Didn't see any symptoms because the belt kept the case in place during firing allowing the shoulder to move forward. Never knew till I tried to fit some of the sized cases into a different 300 win mag.
To make a false shoulder you need a larger sizer ball to expand the neck of the case. You would use a 308 sizer ball. After the entire neck has been expanded run the case back into your 7mm Dakota die reducing some of the neck diameter back to 7mm to a point where the bolt could be closed but with some resistance. The false shoulder keeps the case head against the bolt face and will allow the case to stretch and fill up the shape of the larger chamber.
It would be interesting to fireform one case then section it to study the area just in front of the web to see if it was stretched to a narrower dimension. If you found that to be the situation, your chamber is too long to use safely.
You could section a fired case and look at the area in front in of the web as well.
Probably the best idea is to have a gunsmith reduce the headspace of the rifle. It isn't that hard and doesn't require a reamer.
Let us know what you end up doing.
Ross
varmintH8R
Well-Known Member
I second the above! You can also try the paperclip trick to see if you have case thinning. This article has a pretty practical explanation of looking for signs of web thinning. The Rifleman's Journal: Reloading: Case Head Separations
LONGSHOOTER
Well-Known Member
I prefer the belted mag case.
How to correct excessive headspace?
The gunsmith must make some measurements. A headspace go and no go gauge is used if available. If not the measurements should be able to be accomplished by comparing unsized fired brass vs virgin brass.
The barrel is unscrewed from the reciever using a barrel vise and an action wrench. Then the barrel is centered in a lathe chuck. Metal is machined off the end of the chamber. The same amount of metal is machined from the shoulder moving it forward. If there is an extractor notch in the end of the barrel, it has be indexed and machined deeper for bolt face clearance. If any of these cuts remove more metal than required then a reamer must be used to cut the proper chamber depth to achieve proper headspace.
How do I know this? I did my first barrel with crude measurement devices and cut the chamber too deeply (same as yours, excessive headspace). I then sopme off the end of the barrel to shorten the chamber length and over did that. I then ran in the chamber reamer and went too deep again! I eventually got it. Later on I purchased some tooling to help me make the proper chamber the first time. Nothing like screwing up to truly understand the process.
Basically the entire barrel is set deeper into the reciever with the end result being a shorter chamber.
The gunsmith must make some measurements. A headspace go and no go gauge is used if available. If not the measurements should be able to be accomplished by comparing unsized fired brass vs virgin brass.
The barrel is unscrewed from the reciever using a barrel vise and an action wrench. Then the barrel is centered in a lathe chuck. Metal is machined off the end of the chamber. The same amount of metal is machined from the shoulder moving it forward. If there is an extractor notch in the end of the barrel, it has be indexed and machined deeper for bolt face clearance. If any of these cuts remove more metal than required then a reamer must be used to cut the proper chamber depth to achieve proper headspace.
How do I know this? I did my first barrel with crude measurement devices and cut the chamber too deeply (same as yours, excessive headspace). I then sopme off the end of the barrel to shorten the chamber length and over did that. I then ran in the chamber reamer and went too deep again! I eventually got it. Later on I purchased some tooling to help me make the proper chamber the first time. Nothing like screwing up to truly understand the process.
Basically the entire barrel is set deeper into the reciever with the end result being a shorter chamber.
