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Overpressure and case head growth
- Thread starter hemiford
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Mikecr
Well-Known Member
He's talking about testing for case head expansion that leads to shorter primer pocket life. There are similar tests where measure is compared at the extraction groove, and another at the fired web-line.
He points out that pressure measuring equipment is not actually a final say in this.
And he points out that brass that has yielded, will go right back there (sizing doesn't matter to this).
The useful information is locally measured, and it does not indicate pressure, it's not how to measure pressure, but it can indicate YOUR max load (reloading-wise). People who want their brass to last, measure this stuff. They also look for hard brass alloys, stronger breaches, and lower clearances.
He points out that pressure measuring equipment is not actually a final say in this.
And he points out that brass that has yielded, will go right back there (sizing doesn't matter to this).
The useful information is locally measured, and it does not indicate pressure, it's not how to measure pressure, but it can indicate YOUR max load (reloading-wise). People who want their brass to last, measure this stuff. They also look for hard brass alloys, stronger breaches, and lower clearances.
Calvin45
Well-Known Member
I'm getting to be convinced that those clearances you mention have more of an effect on brass life than anything else, certainly than pressure (unless we're going way over 70k into "brass plasticity" territory).
I have an old savage 99 in .243 that is of sentimental family value. It must have a very loose chamber, even with the light plinking loads it is an absolute BRASS EATER. the whole rear-locking action doesn't help I know. Neck sizing only is an option but doesn't facilitate the most reliable feeding, chambering, and extracting in this old lever gun so I just accept the shorter case life, use inexpensive brass, and don't try to find the limit but just have some good basic fun with the gun from time to time.
Mikecr
Well-Known Member
If 'standard' size is the big side of SAAMI, this will hurt brass reloading life.
I have measured brass that is a bit small per cartridge design, but it hasn't been a problem for me yet. The brass will grow with fire forming and level off where it reasonably should. This, provided I do not exceed what my web-line measure testing (for MyMax) tells me to stay below.
I do this testing because I do not FL size (ever).
The only brass I've ever had pockets loosen with is Norma. Threw it away before I even completed fire forming with it.
Norma's alloy is softer than 'cartridge brass' alloy.
In contrast, brown box Lapua was harder than cartridge brass alloy. That solved a lot of problems for a lot of people.
I have measured brass that is a bit small per cartridge design, but it hasn't been a problem for me yet. The brass will grow with fire forming and level off where it reasonably should. This, provided I do not exceed what my web-line measure testing (for MyMax) tells me to stay below.
I do this testing because I do not FL size (ever).
The only brass I've ever had pockets loosen with is Norma. Threw it away before I even completed fire forming with it.
Norma's alloy is softer than 'cartridge brass' alloy.
In contrast, brown box Lapua was harder than cartridge brass alloy. That solved a lot of problems for a lot of people.
Hugnot
Well-Known Member
Brass used in cartridges is referred to as type 260 brass having a range of percent of copper & zinc alloy content like 68.5-71.5% copper and 28.5-31.5% zinc. This is a relatively narrow range, like 3 %. The amount of zinc would affect hardness, but I am guessing the minor 3% or so variations in copper-zinc content would not be as important as work hardening in affecting brass hardness.
The big question for me is - if the brass is 260 type brass how much zinc content variability among different lots of brass may be expected & how much cold work hardening variability may be expected among different cartridge makers?
The Lapua small primer 6.5X47 brass is real tough & I would expect that it has high zinc content for 260 type brass & maximum work hardening & more brass around primer because of the small primer size.
I use lots of Federal small primer 6.5 CM brass, but the Federal brass does not last as long as Lapua brass. Norma brass has proven to be satisfactory. I use a lot of low cost PPU brass. Measurements to 1/2 thou are tricky & things can happen when measuring, like differences in radii at various measuring locations (no perfect circle). Should primers become real easy to seat the brass has been subjected to tensile forces exceeding elastic limits
The big question for me is - if the brass is 260 type brass how much zinc content variability among different lots of brass may be expected & how much cold work hardening variability may be expected among different cartridge makers?
The Lapua small primer 6.5X47 brass is real tough & I would expect that it has high zinc content for 260 type brass & maximum work hardening & more brass around primer because of the small primer size.
I use lots of Federal small primer 6.5 CM brass, but the Federal brass does not last as long as Lapua brass. Norma brass has proven to be satisfactory. I use a lot of low cost PPU brass. Measurements to 1/2 thou are tricky & things can happen when measuring, like differences in radii at various measuring locations (no perfect circle). Should primers become real easy to seat the brass has been subjected to tensile forces exceeding elastic limits
No correlation would be a brain dead joke. What do those studies think is causing the expansion, if not internal case pressure?
Exposure to the northern lights? Pixie dust???
Obviously it's pressure. But the idea that you can find a measurement to correlate to a certain amount of pressure is what is in question. Also your dealing with a very small measurement which requires a good micrometer and good technique to get a consistent measurement.
He makes some very good points, but I don't see the point in measuring a virgin case. If I'm not mistaken Ken Waters use to measure a fire formed case then allow 1/2 tho beyond this . This seems to make more sense to me. At least that is what I do and I find it seems to give me an idea what I'm doing pressure wise, although it is just another tool to get an idea of pressure like bolt lift , primer apperance etc. JMO
Mikecr
Well-Known Member
cajun is right
You can't get actual pressure (the value) with these measurements.
Likewise, actual pressure is meaningless to results -until you validate results.
It's all useful information, but there is a lot to consider with it.
For instance, if you're running with a sloppy chamber/big clearances, then your brass will expand more (with the same charge pressure).
If your breach is weak, or you don't have adequate barrel steel around the chamber for your cartridge, then your brass will expand more (with the same charge pressure). Excess head spacing and excess firing pin clearance can lead to problems associated with pressure, -while pressure is not the cause. Then you have your barrel -vs- a test barrel. They're not the same.
You can do this testing with either new or fire formed brass. Your criteria and condition will change, but it still works.
If testing with fire formed brass a 1/2thou step change could be a problem for brass life and possibly extraction.
It definitely shows a point where FL sizing will be required in recovery.
I test with new brass & watch it expand as I go up in charge. That expansion levels off, and then eventually step changes up.
It's similar, but my measurement datum is the web-line (widest point on fired case).
I log the charge just prior to the step change point as 'MyMax', as I do not FL size.
This has so far correlated in QL very closely with SAAMI max, but I don't really care about pressure numbers.
I am in local control
A past test of alloys I found out there:
You can't get actual pressure (the value) with these measurements.
Likewise, actual pressure is meaningless to results -until you validate results.
It's all useful information, but there is a lot to consider with it.
For instance, if you're running with a sloppy chamber/big clearances, then your brass will expand more (with the same charge pressure).
If your breach is weak, or you don't have adequate barrel steel around the chamber for your cartridge, then your brass will expand more (with the same charge pressure). Excess head spacing and excess firing pin clearance can lead to problems associated with pressure, -while pressure is not the cause. Then you have your barrel -vs- a test barrel. They're not the same.
You can do this testing with either new or fire formed brass. Your criteria and condition will change, but it still works.
If testing with fire formed brass a 1/2thou step change could be a problem for brass life and possibly extraction.
It definitely shows a point where FL sizing will be required in recovery.
I test with new brass & watch it expand as I go up in charge. That expansion levels off, and then eventually step changes up.
It's similar, but my measurement datum is the web-line (widest point on fired case).
I log the charge just prior to the step change point as 'MyMax', as I do not FL size.
This has so far correlated in QL very closely with SAAMI max, but I don't really care about pressure numbers.
I am in local control
A past test of alloys I found out there:
Thanks Gents, I'm very interested in learning about this critical aspect of safety,
and I don't have anywhere near the experience of others. Great discussion.
In an ideal world, you'd have ideal brass sitting in an ideal chamber.
It's registering that that's not the usual case.
Evidently the fun is how you adapt.
and I don't have anywhere near the experience of others. Great discussion.
In an ideal world, you'd have ideal brass sitting in an ideal chamber.
It's registering that that's not the usual case.
Evidently the fun is how you adapt.
MagnumManiac
Well-Known Member
Good brass, Lapua, Winchester & RWS, all use 70/30 cartridge brass and is the hardest I know of potentially, I'm sure there are others as hard, but as tin content rises, the harder it is.
With the pressure trace, no correlation between brass deformation and pressure could be assumed…soft brass expands at lower pressure and was not traceable linearly in its entirety. Sometimes it would track normally and show nothing, expanded pockets or ejector marks, but when powders changed, and therefore max pressure rise, the brass would fail without an overload.
Nothing in this game is set in stone.
Cheers.
With the pressure trace, no correlation between brass deformation and pressure could be assumed…soft brass expands at lower pressure and was not traceable linearly in its entirety. Sometimes it would track normally and show nothing, expanded pockets or ejector marks, but when powders changed, and therefore max pressure rise, the brass would fail without an overload.
Nothing in this game is set in stone.
Cheers.
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