does the mark/Flow happen before the bullet leaves the brass or is it a couple inches down the barrel or toward the end or a combination of issues ?
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Re: ejector mark Gurus I have a question
Peak pressure (several inches down the barrel), or excessive headspace (oversizing your brass)
Peak pressure (several inches down the barrel), or excessive headspace (oversizing your brass)
Re: ejector mark Gurus I have a question
QuickLoad will provide a good estimate of how many inches down the bore the bullet it when peak pressure hits.
My informed instincts regarding inertia and the mass involved tell me that the brass might not actually "flow" into the less-supported areas (or flatten the headstamp) until some small time after peak pressure. No idea how much, but I'd bet a donut it's measureable.
My own experience is that short-headspaced ammo which breaks cases about 1/2-inch forward of the head will leave very impressive "flow" marks even with loads well below max. My theory is that when the case breaks, it either accelerates that .015 or whatever slop there is to hammer the brass in, or the lack of a braking-effect "grip" from the the rest of the 80% of the case wall increases the thrust of the casehead against the bolt. Maybe some ratio of both, even.
Those same below-max loads in short cases give alarming flattening effects on the primers, but in cases *not* over-sized for the chamber, they keep nice round corners on the primers.
With the possible exception of Federal brass, my opinion is that *any* casehead marks or prints are a sign that pressures are somewhere north of 60K PSI. I abandon all loads that do such.
YMMV
QuickLoad will provide a good estimate of how many inches down the bore the bullet it when peak pressure hits.
My informed instincts regarding inertia and the mass involved tell me that the brass might not actually "flow" into the less-supported areas (or flatten the headstamp) until some small time after peak pressure. No idea how much, but I'd bet a donut it's measureable.
My own experience is that short-headspaced ammo which breaks cases about 1/2-inch forward of the head will leave very impressive "flow" marks even with loads well below max. My theory is that when the case breaks, it either accelerates that .015 or whatever slop there is to hammer the brass in, or the lack of a braking-effect "grip" from the the rest of the 80% of the case wall increases the thrust of the casehead against the bolt. Maybe some ratio of both, even.
Those same below-max loads in short cases give alarming flattening effects on the primers, but in cases *not* over-sized for the chamber, they keep nice round corners on the primers.
With the possible exception of Federal brass, my opinion is that *any* casehead marks or prints are a sign that pressures are somewhere north of 60K PSI. I abandon all loads that do such.
YMMV
Re: ejector mark Gurus I have a question
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Grump</div><div class="ubbcode-body">My informed instincts regarding inertia and the mass involved tell me that the brass might not actually "flow" into the less-supported areas (or flatten the headstamp) until some small time after peak pressure. No idea how much, but I'd bet a donut it's measureable.</div></div>
My instincts tell me that as the pressure rises near 58K PSI the brass changes from being a stiff substance into a plastic substance (think bees wax). While plastic it will yield to the pressure, the pressure can cause the brass to flow in any direction that will (help) relieve the pressure (into the bolt face). As the pressure drops under 58K PSI the brass returns to its stiff state.
The rate of flow is easily computed by determining the viscosity of the brass in its plastic state under pressure. However, the entire peak of the pressure cuve is in the dozen to couple dozen microseconds for sane loads. Maybe approaching 60-70 microseconds for loads on the very edge of sanity. More time and or pressure than this and the brass will flow into the bolt face and the case wall will be visibly distorted. {And this may ven be on the long side}
For most (sane) loads the bullet has left the neck and is 1-3 inches down the tube.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Grump</div><div class="ubbcode-body">My informed instincts regarding inertia and the mass involved tell me that the brass might not actually "flow" into the less-supported areas (or flatten the headstamp) until some small time after peak pressure. No idea how much, but I'd bet a donut it's measureable.</div></div>
My instincts tell me that as the pressure rises near 58K PSI the brass changes from being a stiff substance into a plastic substance (think bees wax). While plastic it will yield to the pressure, the pressure can cause the brass to flow in any direction that will (help) relieve the pressure (into the bolt face). As the pressure drops under 58K PSI the brass returns to its stiff state.
The rate of flow is easily computed by determining the viscosity of the brass in its plastic state under pressure. However, the entire peak of the pressure cuve is in the dozen to couple dozen microseconds for sane loads. Maybe approaching 60-70 microseconds for loads on the very edge of sanity. More time and or pressure than this and the brass will flow into the bolt face and the case wall will be visibly distorted. {And this may ven be on the long side}
For most (sane) loads the bullet has left the neck and is 1-3 inches down the tube.
Re: ejector mark Gurus I have a question
OK I got better response than expect,Thank you fellas.
Now I have an 18.5" barrel and a load that is fine temp stable gets pressure with a can ,this Leeds me to believe the ejector marks may be a combination of ignition pressure and barrel residual pressure any thoughts ?
OK I got better response than expect,Thank you fellas.
Now I have an 18.5" barrel and a load that is fine temp stable gets pressure with a can ,this Leeds me to believe the ejector marks may be a combination of ignition pressure and barrel residual pressure any thoughts ?
Re: ejector mark Gurus I have a question
What is barrel residual pressure?
If your brass is properly sized and your getting ejector marks you need to back off a minimum of 1/2 to one grain.
What is barrel residual pressure?
If your brass is properly sized and your getting ejector marks you need to back off a minimum of 1/2 to one grain.
Re: ejector mark Gurus I have a question
Increase pressure is a better word and what i could have said..
What I am looking for here , does barrel length have anything to do with ejector marks or is it at ignition before it leaves the hull.
Increase pressure is a better word and what i could have said..
What I am looking for here , does barrel length have anything to do with ejector marks or is it at ignition before it leaves the hull.
Re: ejector mark Gurus I have a question
Barrel residual pressure is sooooo low compared to peak (try 10KPSI), that pressure signs from adding a can has to be from some other effect earlier in the firing cycle.
Remember, .454 Casull revolvers can show brass flow, with barrels only 8-10 inches long. That cartridge runs at rifle pressures.
The only real way to pin this down would be to glue a Pressure Trace system to your barrel's chamber area and compare what the instrumentation gives you, shooting with and without the can.
Your chosen load just may be over pressure specs. As I understand it, some rifle/component combinations don't show "signs" of high pressure until significantly above SAAMI pressures have been exceeded.
Barrel residual pressure is sooooo low compared to peak (try 10KPSI), that pressure signs from adding a can has to be from some other effect earlier in the firing cycle.
Remember, .454 Casull revolvers can show brass flow, with barrels only 8-10 inches long. That cartridge runs at rifle pressures.
The only real way to pin this down would be to glue a Pressure Trace system to your barrel's chamber area and compare what the instrumentation gives you, shooting with and without the can.
Your chosen load just may be over pressure specs. As I understand it, some rifle/component combinations don't show "signs" of high pressure until significantly above SAAMI pressures have been exceeded.
Re: ejector mark Gurus I have a question
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ASM1</div><div class="ubbcode-body">What I am looking for here , does barrel length have anything to do with ejector marks or is it at ignition before it leaves the hull. </div></div>
As long as you stay away from the secondary pressure spike from underloaded rounds,
The markings on the cases from pressure happen in the first 3-5" of the barrel.
THe secondary pressure spike is a detonation event in the barrel where the supersonic blast wave reaches the back of the decelerating bullet in the barrel and sets up a shock wave whch detonates the residual powder and creates very high pressure levels. See:
http://www.shootingsoftware.com/barrel.htm
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ASM1</div><div class="ubbcode-body">What I am looking for here , does barrel length have anything to do with ejector marks or is it at ignition before it leaves the hull. </div></div>
As long as you stay away from the secondary pressure spike from underloaded rounds,
The markings on the cases from pressure happen in the first 3-5" of the barrel.
THe secondary pressure spike is a detonation event in the barrel where the supersonic blast wave reaches the back of the decelerating bullet in the barrel and sets up a shock wave whch detonates the residual powder and creates very high pressure levels. See:
http://www.shootingsoftware.com/barrel.htm
Re: ejector mark Gurus I have a question
Guys I cant thank you enough this information is what I was after..
Frankie...
Guys I cant thank you enough this information is what I was after..
Frankie...
Re: ejector mark Gurus I have a question
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: criver</div><div class="ubbcode-body">Peak pressure (several inches down the barrel), or excessive headspace (oversizing your brass) </div></div>
Or case lube left on the case when fired or, Cases that need to be trimmed or , lube left in the chamber after cleaning, can all cause the case to show signs of excess pressure as well.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: criver</div><div class="ubbcode-body">Peak pressure (several inches down the barrel), or excessive headspace (oversizing your brass) </div></div>
Or case lube left on the case when fired or, Cases that need to be trimmed or , lube left in the chamber after cleaning, can all cause the case to show signs of excess pressure as well.
Re: ejector mark Gurus I have a question
I have a question for you guys. As you're working your way up with powder charges, what pressure signs should start appearing first, flat primers or swipes?
I have a question for you guys. As you're working your way up with powder charges, what pressure signs should start appearing first, flat primers or swipes?
Re: ejector mark Gurus I have a question
Ejector swipes on the head and noticably harder bolt lift are more telling than primer flattening as there are other sources for flattening then just high pressure.
Ejector swipes on the head and noticably harder bolt lift are more telling than primer flattening as there are other sources for flattening then just high pressure.
Re: ejector mark Gurus I have a question
If you're reading primers, get an idea for what they look like under normal pressures first.
My AR primer firing pin strikes look a bit cratered with normal loads; I get no additional pressure signs until they blow out.
If you're reading primers, get an idea for what they look like under normal pressures first.
My AR primer firing pin strikes look a bit cratered with normal loads; I get no additional pressure signs until they blow out.
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