Case dimensions outside SAAMI minimums-what's the risk?
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Case dimensions outside SAAMI minimums-what's the risk?
What's the risk of reloading once fired cases with headspace below SAAMI minimums, but overall case length is within specs, and final OAL with seated bullet will be within specs as well?
Re: Case dimensions outside SAAMI minimums-what's the risk?
If I understand your question, It's one of headspace.
On firing, any cartridge inflates like a balloon until it takes up the space allowed by the chamber. The brass itself is just a jig that hold everything together but doesn't do much to contain the pressure on it's own. If there's too much headspace the "balloon" takes material from parts of the case to inflate. Since the case head is pushed back against the bolt that "balloon" material comes from in front of the case head. If headspace is bad enough you could have a catastrophic failure with a case head separation. If the condition is less pronounced and it's repeated over time you can get an insipient case head separation. Sometimes this can be seen from the outside of the case as a bright ring. But it can also be felt inside the case with a bent paperclip.
How much is a danger? I have no idea. Maybe someone else knows.
The ideal condition is where the case has a perfect fit to the chamber, but in a semi-auto that perfect fit has to be tempered with allowance for things not being perfect since it's only a spring that closes the action. But in a bolt action if the brass is fired out of that one bolt action neck sizing only works fine. Any final "sizing" of the brass is done by the camming action of the bolt closing by human power.
On firing, any cartridge inflates like a balloon until it takes up the space allowed by the chamber. The brass itself is just a jig that hold everything together but doesn't do much to contain the pressure on it's own. If there's too much headspace the "balloon" takes material from parts of the case to inflate. Since the case head is pushed back against the bolt that "balloon" material comes from in front of the case head. If headspace is bad enough you could have a catastrophic failure with a case head separation. If the condition is less pronounced and it's repeated over time you can get an insipient case head separation. Sometimes this can be seen from the outside of the case as a bright ring. But it can also be felt inside the case with a bent paperclip.
How much is a danger? I have no idea. Maybe someone else knows.
The ideal condition is where the case has a perfect fit to the chamber, but in a semi-auto that perfect fit has to be tempered with allowance for things not being perfect since it's only a spring that closes the action. But in a bolt action if the brass is fired out of that one bolt action neck sizing only works fine. Any final "sizing" of the brass is done by the camming action of the bolt closing by human power.
Re: Case dimensions outside SAAMI minimums-what's the risk?
Thank you for the reply. It would seem therefore that a catastrophic failure is more likely if the headspace dimension is significantly less than minimum, which does make sense.
So now for my confession...so that others may learn from my screwup.
I have several thousand once/twice fired cases with wildly mixed head stamps (culled out the 223/556 converts). After cleaning, I had started full length sizing and decapping and was randomly checking fit with a Sheridan cutaway gauge. All fit nicely, at least to my eye. Case mouth snugly up against the chamber rim, no space between the shoulder and the gauge. As Ace Ventura would say, " Like a Glove!" An occasional glance at the case head in the slot of the gauge looked OK. I should have paid more attention to the gauge groove in the head. After about 250 cases, I realized the case head was below slot in the gauge. I did some actual headspace measurements, compared those with the unsized cases and with some new Remington loaded rounds and realized I had not been careful in setting the resizing die. I had pushed the shoulders back .011 on average, although the average case length was not pushed below minimums.(average case length 1.361, SD .005)
My plan is to resize these cases, again, with the die properly adjusted in the press, and hope for enough stretch to get back to minimums. Is this a bad plan? I will specially mark these cases because they will have undergone some extra case hardening compared to the remaining cases and are more likely to start showing signs of potential failure sooner than the rest. I am also going to inspect these much more carefully for any signs of weakening that I otherwise might have tolerated.
"The foolish learn from their own mistakes, the wise learn from the mistakes of others." - me
So now for my confession...so that others may learn from my screwup.
I have several thousand once/twice fired cases with wildly mixed head stamps (culled out the 223/556 converts). After cleaning, I had started full length sizing and decapping and was randomly checking fit with a Sheridan cutaway gauge. All fit nicely, at least to my eye. Case mouth snugly up against the chamber rim, no space between the shoulder and the gauge. As Ace Ventura would say, " Like a Glove!" An occasional glance at the case head in the slot of the gauge looked OK. I should have paid more attention to the gauge groove in the head. After about 250 cases, I realized the case head was below slot in the gauge. I did some actual headspace measurements, compared those with the unsized cases and with some new Remington loaded rounds and realized I had not been careful in setting the resizing die. I had pushed the shoulders back .011 on average, although the average case length was not pushed below minimums.(average case length 1.361, SD .005)
My plan is to resize these cases, again, with the die properly adjusted in the press, and hope for enough stretch to get back to minimums. Is this a bad plan? I will specially mark these cases because they will have undergone some extra case hardening compared to the remaining cases and are more likely to start showing signs of potential failure sooner than the rest. I am also going to inspect these much more carefully for any signs of weakening that I otherwise might have tolerated.
"The foolish learn from their own mistakes, the wise learn from the mistakes of others." - me
Re: Case dimensions outside SAAMI minimums-what's the risk?
This should never happen.Okiedelta wrote: ↑Tue Feb 23, 2021 1:28 pm Thank you for the reply. It would seem therefore that a catastrophic failure is more likely if the headspace dimension is significantly less than minimum, which does make sense.
So now for my confession...so that others may learn from my screwup.
I have several thousand once/twice fired cases with wildly mixed head stamps (culled out the 223/556 converts). After cleaning, I had started full length sizing and decapping and was randomly checking fit with a Sheridan cutaway gauge. All fit nicely, at least to my eye. Case mouth snugly up against the chamber rim, no space between the shoulder and the gauge. As Ace Ventura would say, " Like a Glove!" An occasional glance at the case head in the slot of the gauge looked OK. I should have paid more attention to the gauge groove in the head. After about 250 cases, I realized the case head was below slot in the gauge. I did some actual headspace measurements, compared those with the unsized cases and with some new Remington loaded rounds and realized I had not been careful in setting the resizing die. I had pushed the shoulders back .011 on average, although the average case length was not pushed below minimums.(average case length 1.361, SD .005)
My plan is to resize these cases, again, with the die properly adjusted in the press, and hope for enough stretch to get back to minimums. Is this a bad plan? I will specially mark these cases because they will have undergone some extra case hardening compared to the remaining cases and are more likely to start showing signs of potential failure sooner than the rest. I am also going to inspect these much more carefully for any signs of weakening that I otherwise might have tolerated.
"The foolish learn from their own mistakes, the wise learn from the mistakes of others." - me
When the case neck stretches into the chamber, it will pinch the bullet and cause pressure spikes.
If your brass is sized properly to max base to shoulder datum length, which is minimum headspace, there should be a .010" gap from the end of the neck and the step in the chamber.
The other potential problem of setting the shoulders back too far, is that the cartridge may end up headspacing off the bullet, so be aware of that, because your chamber is different than the gauge.
Running them through the same die again will change nothing, unless you have another expander that will allow you to open up the case and reform the shoulder.
If you are going to shoot them, a low pressure sub round would be the best.
Keep in mind that they might not even fire if the shoulder is set back so far that the firing pin can not hit the primer
300 Blackout, not just for sub-sonics.
Re: Case dimensions outside SAAMI minimums-what's the risk?
Was all the brass fired in your gun(s)‽
What is extra case hardening?
What is extra case hardening?
Re: Case dimensions outside SAAMI minimums-what's the risk?
None of the cases were fired in my gun. These were bulk range brass I ordered from Capital Cartridge in Austin Tx.
Extra case hardening referred to the brass that would come from trying to lengthen the case by resizing in a proper die set up.
Extra case hardening referred to the brass that would come from trying to lengthen the case by resizing in a proper die set up.
Re: Case dimensions outside SAAMI minimums-what's the risk?
Fitting in the gauge only tells you one thing; that the case fits in the gauge.
If it were me, I'd load one, shoot it, and compare that case's measurements to an unfired case.
If it were me, I'd load one, shoot it, and compare that case's measurements to an unfired case.
Re: Case dimensions outside SAAMI minimums-what's the risk?
Goos solution it seems to me. I plan to measure the headspace on all the 250 cases. The data I hit came from a small sample.
For cases that headspace shorter than SAAMI minimum,will there be a potential issue with extraction?
For cases that headspace shorter than SAAMI minimum,will there be a potential issue with extraction?
Re: Case dimensions outside SAAMI minimums-what's the risk?
It's not likely you'll have any particular extraction issues.
Upon firing, your short-headspace rounds will expand once again to match your rifle's chamber dimensions... and then will spring back a bit.
Assuming the rounds ignite at all - note dellet's comment - the first risk you face is a bullet being pinched because the round has ridden too far into the chamber... or that the bullet has jammed unexpectedly into the rifling.
The second risk would be a case head separation.
If you want to try and salvage that brass, I'd do what dellet suggested and load them with a very light load. I'd also use a short, light bullet.
Upon firing, your short-headspace rounds will expand once again to match your rifle's chamber dimensions... and then will spring back a bit.
Assuming the rounds ignite at all - note dellet's comment - the first risk you face is a bullet being pinched because the round has ridden too far into the chamber... or that the bullet has jammed unexpectedly into the rifling.
The second risk would be a case head separation.
If you want to try and salvage that brass, I'd do what dellet suggested and load them with a very light load. I'd also use a short, light bullet.
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