tight bolt close
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JeepHammer
Moderator
You said it yourself, stretch.
I think (and this is just what I think) the powder burns rear to front.
The primer ignites the powder, pressure builds as the powder burns rear to front.
Time is a factor here, the powder must burn and the burn must have time, even a millisecond to transfer heat from burn into expansion.
(That's why it's called 'Thermal Expansion')
In my model, remaining powder is forced forward against the shoulder.
Keep in mind here not all powder burns, if it did, when you shoot cardboard in front of the muzzle you wouldn't find unburned powder & powder that stuck & burned in the cardboard.
So, unburned powder and pressure are pushing on the shoulder & back of the case, since side walls will be the first to bloat and hit the walls of the chamber...
The shoulder moves forward, relative to case head.
This model means the back of the powder chamber heats most, and sees the most pressure.
Most case head separations I see are just above the web at the bottom of the powder chamber, this would be exactly where the case would stretch most, and thin most in this model.
Keep in mind that brass becomes very weak at just over 750-800*F, and the rear of the powder chamber will see the most heat 'Soak' time (being exposed to the first of the burn, well before the bullet moves).
What saves the case is thermal transfer, heat soaks brass, brass then transfer heat to chamber.
Chamber works like a heat sink and saves brass.
The overpressure & overheating of the brass before the brass swells enough to contact chamber walls would also explain why the case swells well into the web where it's so damned difficult to get out.
I've seen endless postulation on how powder burns, but the fact of the matter is, it doesn't all burn simply because you get a muzzle blast, and in stop motion photography show 'Sparks', grains of powder burning outside the muzzle.
Now, this is pretty conclusive it's not just heat/plasma escaping and all the powder burned like some people think.
It's by far not all 'Hot Carbon' by the time it exits the muzzle as some claim...
I can be totally off base, anything is possible, but this explains how case heads separate where they do, and how they do.
I can't believe a case can become 'Locked' into a chamber so tightly that case stretch, or bullet departure and rearward recoil force can't dislodge it.
I've tried to move a bullet in a barrel after it was sized to the rifling (squib removal) and you have to use hydraulic force or a REALLY big hammer, and that's AFTER it's sized, just overcoming the interference fit between bullet & barrel.
I think (and this is just what I think) the powder burns rear to front.
The primer ignites the powder, pressure builds as the powder burns rear to front.
Time is a factor here, the powder must burn and the burn must have time, even a millisecond to transfer heat from burn into expansion.
(That's why it's called 'Thermal Expansion')
In my model, remaining powder is forced forward against the shoulder.
Keep in mind here not all powder burns, if it did, when you shoot cardboard in front of the muzzle you wouldn't find unburned powder & powder that stuck & burned in the cardboard.
So, unburned powder and pressure are pushing on the shoulder & back of the case, since side walls will be the first to bloat and hit the walls of the chamber...
The shoulder moves forward, relative to case head.
This model means the back of the powder chamber heats most, and sees the most pressure.
Most case head separations I see are just above the web at the bottom of the powder chamber, this would be exactly where the case would stretch most, and thin most in this model.
Keep in mind that brass becomes very weak at just over 750-800*F, and the rear of the powder chamber will see the most heat 'Soak' time (being exposed to the first of the burn, well before the bullet moves).
What saves the case is thermal transfer, heat soaks brass, brass then transfer heat to chamber.
Chamber works like a heat sink and saves brass.
The overpressure & overheating of the brass before the brass swells enough to contact chamber walls would also explain why the case swells well into the web where it's so damned difficult to get out.
I've seen endless postulation on how powder burns, but the fact of the matter is, it doesn't all burn simply because you get a muzzle blast, and in stop motion photography show 'Sparks', grains of powder burning outside the muzzle.
Now, this is pretty conclusive it's not just heat/plasma escaping and all the powder burned like some people think.
It's by far not all 'Hot Carbon' by the time it exits the muzzle as some claim...
I can be totally off base, anything is possible, but this explains how case heads separate where they do, and how they do.
I can't believe a case can become 'Locked' into a chamber so tightly that case stretch, or bullet departure and rearward recoil force can't dislodge it.
I've tried to move a bullet in a barrel after it was sized to the rifling (squib removal) and you have to use hydraulic force or a REALLY big hammer, and that's AFTER it's sized, just overcoming the interference fit between bullet & barrel.
Keep in mind that the pressure is the same in every direction. So the force against the case walls (and subsequently against the chamber) is the greater than the force against the base of the bullet or bottom of the case. (The greater the area, the greater the force).
During firing, the base of the case ends up against the bolt face in one of two ways (EDIT: assuming there is some clearance between case and chamber/bolt). If the pressure is great enough the case stretches in the web area until it hits the bolt face. If the pressure isn't enough to stretch the case in the web area, the case is driven back against the bolt face as the bullet exits the barrel and the pressure drops enough for the case walls to release from the chamber and allow the case slide back against the bolt face.
A case moving back against the bolt face early in the firing sequence would be a very bad, since that would mean high pressure gas would also be able to escape reward at the same time. Instead, the case is held tightly against the chamber by great force very early in the firing sequence, effectively sealing the case body against the inside of the chamber.
During firing, the base of the case ends up against the bolt face in one of two ways (EDIT: assuming there is some clearance between case and chamber/bolt). If the pressure is great enough the case stretches in the web area until it hits the bolt face. If the pressure isn't enough to stretch the case in the web area, the case is driven back against the bolt face as the bullet exits the barrel and the pressure drops enough for the case walls to release from the chamber and allow the case slide back against the bolt face.
A case moving back against the bolt face early in the firing sequence would be a very bad, since that would mean high pressure gas would also be able to escape reward at the same time. Instead, the case is held tightly against the chamber by great force very early in the firing sequence, effectively sealing the case body against the inside of the chamber.
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or refuse to believe:
Again: I like a chamber that reflects the image of the rifling in the barrel. I do not want cross hatching and or spiral cuts; I understand most believe a rough surface has more grip, not me. I prefer a 100% contact, when it comes to case hold in the chamber nothing says it better than 100% contact between the case and chamber than 100%.
And there are all of those PSIs, 10s of thousands of them, what is the infatuation with greasing your bullet, case and chamber if not for the case locking onto the chamber wall? Slide and glide shooters thought it was a great way to fire form cases. One of the ugliest threads ever was committed on a bench rester forum. That one went for 40 pages, there was no room for decency; the winner? The winner was the most rude, vulgar and in my opinion based on my observation the most socially dysfunctional. All of those that could be intimidated were afraid of him and that made him worst. If a poster did not agree with him he would insult the poster until the poster.... it should not have been that way.
He was anti-grease your bullet, case and chamber.
F. Guffey
Again: I like a chamber that reflects the image of the rifling in the barrel. I do not want cross hatching and or spiral cuts; I understand most believe a rough surface has more grip, not me. I prefer a 100% contact, when it comes to case hold in the chamber nothing says it better than 100% contact between the case and chamber than 100%.
And there are all of those PSIs, 10s of thousands of them, what is the infatuation with greasing your bullet, case and chamber if not for the case locking onto the chamber wall? Slide and glide shooters thought it was a great way to fire form cases. One of the ugliest threads ever was committed on a bench rester forum. That one went for 40 pages, there was no room for decency; the winner? The winner was the most rude, vulgar and in my opinion based on my observation the most socially dysfunctional. All of those that could be intimidated were afraid of him and that made him worst. If a poster did not agree with him he would insult the poster until the poster.... it should not have been that way.
He was anti-grease your bullet, case and chamber.
F. Guffey
I agree, the firing pin is mechanical, the powder when contained goes fast; now we should consider time as a factor.
Some believe it is a wrinkle or a progressive increase in pressure from the case head to the neck of the case. NECK OF THE CASE
The case neck releases the bullet before the bullet has it's run at the rifling.Back in the old days they built cases with tubes that extended from the flash hole to the top of the powder column in an effort to ignite the powder behind the projectile first. Somewhere around here I have a cannon shell with the long tube that extends the flash.
F. Guffey
JeepHammer
Moderator
Pressure is the same in every direction. Fact, no question.
Forward in the case pressure is pushing a solid against the shoulder since a rifle case is more or less full.
It's a fairly fine grain solid that will often pack and stick together.
Anyone this has torn down loads has seen the clumps.
With modern powders, the loads are often compressed. No real air space left in the case to speak of.
I point to black powder cases that often aren't full and need filler to keep the powder burning and not allowing the entire powder charge to burn at once.
I learned that one the hard way using hollow based bullets and destroying the revolver.
I still can't see a firing pin holding a case forward.
First the primer is very soft and it's already clearance from the pin strike. I can't see that primer holding the force of recoil.
Just decapping force often pushes the firing pin dent mostly back out, and there is the primer anvil in the way, spreading the decapping pin force out when decapping.
Like I said, it's a working theroy from observation,
The banding/thinning/pitting of the brass in the bottom of the powder chamber, precisely where the powder burns first and the case gets the hottest.
Heat concentration causing the pitting & banding from stretching at that small area.
The intense pressure that has to build to size the bullet in the throat is way more than sufficency to overcome any sticking the case might with the chamber walls.
Keep in mind the bullet has started to move by the time it reaches the throat, so case recoil is in full swing at this point in the process.
To say a case sticks to the chamber walls during firing would also mean you wouldn't need the bolt in place at all since the case would hold itself in place in the chamber during firing cycle.
It would simply release after the bullet exits the barrel, more or less...
I've sectioned a LOT of cases for material inspection (hardness testing, micrographs), and to look for changes in design & materials from year to year or manufacturer to manufacturer, I've done a lot of sections to see what repeated reloading does to cases, mostly to figure out when I should scrap cases so they don't fail in the chamber...
--- One thing I keep coming back to, there wouldn't be any reloading if the cases weren't overbuilt in the first place...
The rear of that case ALWAYS takes more of a beating from firing than any other part.
It's stretched (you guys know the paper clip test), it's pitted, it's carbonized, and I don't even want to guess what temprature it takes to carbonize brass!
The necks get 'Warbles' with repeated reloading, this is from the reloading process.
The case stretches at the lower walls, the resizing die forces the extra length up the case to the neck where we trim it off. All resizing, not the firing process.
While you see unseated primers and think the brass wasn't against the bolt face, I see a primer in a slip fit pocket that can get knocked loose at any time during the firing-eject cycle.
What I see is brass migration from head to rim, I see headstamps Being hit hard enough to flatten the head material and make it migrate out to rim & into extraction groove, lower head & web bloating from migrating brass & huge pressure/heat loading during the firing cycle.
The ejection is a cake walk compared to what the case takes in the chamber, I've seen ejection equivalent force yank primers, every time I work the press handle in fact,
But I've never seen ejection equivalent force make brass 'Plastic' and flow...
If anyone has a better explanation for brass migration, particularly downward in the head, I'll give it my full attention. Right now this is my working theroy, and it accounts for what the brass does, from pitting/carbonizing to bloating to hammering the head out oversize, to blowing primer pockets out oversize...
Every Reloader seems to fixate on the parts of the case they bend. It's natural since that's the part they see, inspect, handle and move around.
When I started sectioning cases, that's when the head scratching began...
When I started to recondition brass and had to measure rims, grooves, web that's when I realized something was going on I had completely ignored.
When I started to produce new brass, that's when I started to understand the force it takes to make brass 'Plastic', what force it takes to make solid brass in the head migrate.
(And, like every beginner, I had to hire an actual expert to continue since I was WAY out of my education zone and well beyond the point of my understanding).
Cases were created through trial & error, there have been brass (naturally), zinc, aluminum, tin, steel, copper, lead and even ductile iron that I know about. There is probably a lot more materials I have no idea about tried.
I can't even guess how many different alloys were tested/tried!
Now it's a science, the science has settled on 'High' brass as a common case material, probably because it holds up and humans understand how to work it efficiently.
I'm just chasing the evidence since I don't have a degree in metallurgy specialising in Non-ferrous metals, specifically brass alloys.
I'm doing observation, and trying to extrapolate what exactly the frack is happening to my cases!
Forward in the case pressure is pushing a solid against the shoulder since a rifle case is more or less full.
It's a fairly fine grain solid that will often pack and stick together.
Anyone this has torn down loads has seen the clumps.
With modern powders, the loads are often compressed. No real air space left in the case to speak of.
I point to black powder cases that often aren't full and need filler to keep the powder burning and not allowing the entire powder charge to burn at once.
I learned that one the hard way using hollow based bullets and destroying the revolver.
I still can't see a firing pin holding a case forward.
First the primer is very soft and it's already clearance from the pin strike. I can't see that primer holding the force of recoil.
Just decapping force often pushes the firing pin dent mostly back out, and there is the primer anvil in the way, spreading the decapping pin force out when decapping.
Like I said, it's a working theroy from observation,
The banding/thinning/pitting of the brass in the bottom of the powder chamber, precisely where the powder burns first and the case gets the hottest.
Heat concentration causing the pitting & banding from stretching at that small area.
The intense pressure that has to build to size the bullet in the throat is way more than sufficency to overcome any sticking the case might with the chamber walls.
Keep in mind the bullet has started to move by the time it reaches the throat, so case recoil is in full swing at this point in the process.
To say a case sticks to the chamber walls during firing would also mean you wouldn't need the bolt in place at all since the case would hold itself in place in the chamber during firing cycle.
It would simply release after the bullet exits the barrel, more or less...
I've sectioned a LOT of cases for material inspection (hardness testing, micrographs), and to look for changes in design & materials from year to year or manufacturer to manufacturer, I've done a lot of sections to see what repeated reloading does to cases, mostly to figure out when I should scrap cases so they don't fail in the chamber...
--- One thing I keep coming back to, there wouldn't be any reloading if the cases weren't overbuilt in the first place...
The rear of that case ALWAYS takes more of a beating from firing than any other part.
It's stretched (you guys know the paper clip test), it's pitted, it's carbonized, and I don't even want to guess what temprature it takes to carbonize brass!
The necks get 'Warbles' with repeated reloading, this is from the reloading process.
The case stretches at the lower walls, the resizing die forces the extra length up the case to the neck where we trim it off. All resizing, not the firing process.
While you see unseated primers and think the brass wasn't against the bolt face, I see a primer in a slip fit pocket that can get knocked loose at any time during the firing-eject cycle.
What I see is brass migration from head to rim, I see headstamps Being hit hard enough to flatten the head material and make it migrate out to rim & into extraction groove, lower head & web bloating from migrating brass & huge pressure/heat loading during the firing cycle.
The ejection is a cake walk compared to what the case takes in the chamber, I've seen ejection equivalent force yank primers, every time I work the press handle in fact,
But I've never seen ejection equivalent force make brass 'Plastic' and flow...
If anyone has a better explanation for brass migration, particularly downward in the head, I'll give it my full attention. Right now this is my working theroy, and it accounts for what the brass does, from pitting/carbonizing to bloating to hammering the head out oversize, to blowing primer pockets out oversize...
Every Reloader seems to fixate on the parts of the case they bend. It's natural since that's the part they see, inspect, handle and move around.
When I started sectioning cases, that's when the head scratching began...
When I started to recondition brass and had to measure rims, grooves, web that's when I realized something was going on I had completely ignored.
When I started to produce new brass, that's when I started to understand the force it takes to make brass 'Plastic', what force it takes to make solid brass in the head migrate.
(And, like every beginner, I had to hire an actual expert to continue since I was WAY out of my education zone and well beyond the point of my understanding).
Cases were created through trial & error, there have been brass (naturally), zinc, aluminum, tin, steel, copper, lead and even ductile iron that I know about. There is probably a lot more materials I have no idea about tried.
I can't even guess how many different alloys were tested/tried!
Now it's a science, the science has settled on 'High' brass as a common case material, probably because it holds up and humans understand how to work it efficiently.
I'm just chasing the evidence since I don't have a degree in metallurgy specialising in Non-ferrous metals, specifically brass alloys.
I'm doing observation, and trying to extrapolate what exactly the frack is happening to my cases!
JeepHammer
Moderator
Guffy, I want answers, not third grade name calling.
There are plenty of oversized children, I don't have to join that demographic.
I have a job, I get things done, I have a higher functioning brain, my education didn't come from YouTube videos & facebag memes...
I'm NOT Archimedes, DaVinci, Einstein, Tesla, Hawking, so the only way I'm going to figure things out is by reading & connecting with other humans.
I bend, drill, turn metal to make machines. I make pretty good machines, but everything I'd do is based on real genius that defined & quantified the factors required for what I do, and they wrote it all down...
Books, like video, only for actually smart & capable people.
I'm proud of my library, the machines either work or they are a learning experience, and I know a good idea when I steal it!
MG, how does your firing pin theroy stand up against spring loaded firing pins, inertia firing pins that aren't as long as the pin bore, strikers, etc.?
I'm not being a prick, I actually want to know.
A 'Free' firing pin will strike & rebound back into the bore,
A striker can't reach the primer in the resting position,
Neither can a spring pin or inertia pin.
All will retract as soon as they strike the primer...
Something like an AR, the hammer will hold firing pin out, but even old revolvers with firing pin on hammer have resting positions where pin doesn't make contact with primer.
Even the oldest shot guns & rifles with external hammers had a resting point that kept the hammer off the firing pin, the pins had springs to retract them.
(Otherwise just closing the bolt could set the round off, which I have to assume, is why 'Rest' notches on hammers were invented!)
This ASSUMES the bores & pins are clean & properly sized, functioning as designed...
There are plenty of oversized children, I don't have to join that demographic.
I have a job, I get things done, I have a higher functioning brain, my education didn't come from YouTube videos & facebag memes...
I'm NOT Archimedes, DaVinci, Einstein, Tesla, Hawking, so the only way I'm going to figure things out is by reading & connecting with other humans.
I bend, drill, turn metal to make machines. I make pretty good machines, but everything I'd do is based on real genius that defined & quantified the factors required for what I do, and they wrote it all down...
Books, like video, only for actually smart & capable people.
I'm proud of my library, the machines either work or they are a learning experience, and I know a good idea when I steal it!
MG, how does your firing pin theroy stand up against spring loaded firing pins, inertia firing pins that aren't as long as the pin bore, strikers, etc.?
I'm not being a prick, I actually want to know.
A 'Free' firing pin will strike & rebound back into the bore,
A striker can't reach the primer in the resting position,
Neither can a spring pin or inertia pin.
All will retract as soon as they strike the primer...
Something like an AR, the hammer will hold firing pin out, but even old revolvers with firing pin on hammer have resting positions where pin doesn't make contact with primer.
Even the oldest shot guns & rifles with external hammers had a resting point that kept the hammer off the firing pin, the pins had springs to retract them.
(Otherwise just closing the bolt could set the round off, which I have to assume, is why 'Rest' notches on hammers were invented!)
This ASSUMES the bores & pins are clean & properly sized, functioning as designed...
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Some notes from todays shoot. as I assumed the shoulder was out by .008 ->.010 (confirmed by nick in the 3rd post). at +.008 I can close the bolt with some resistance but at .010 the rifle said no way, as did I. Not sure where things shifted in my die / press setup, rather irrelevant at this point. SD looked like crap on the loads tested today, think it has something to do with the available sunlight constantly changing or my cheep chronograph. All holes in holes at 50 yrds. Range was open to public today, couldn't setup at 200m. Some interesting things popped out at me while recording my notes, but that's for another post. please forgive the poor penmanship on my notes, just a quick hand written thing.
Thanks for the input, was a good learning experience. Now I need to repeat the process with the 700p and make note of its chamber so I don't do this again.
Joe G
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Reloaders are becoming too selective when it comes to what they want to hear.
The pressure inside the case can force the firing pin back by overcoming the spring pressure: and do not forget the spring can have 17 pounds of pressure, the pressure inside the case be 50.000 +/-
. That has got to have something to do with the .7854 thing
And then there is the dent, the dent in the primer is not the same dent a reloaders sees when he examines the case. When pressure increases inside the case the primer conforms to the firing pin nose because of the increase in pressure. And then there is blanking
, Some reloaders have are required to stop shooting when their receivers fill with stamped out plugs from the primer blanking
. I know, it sounds cool; 'primer blanking', all that is required is 5 reloaders that do does not understand what is going on to agree to make it a fact.F. Guffey
King Kong primers
If the primmer is tuff enough to support all of that pressure how is it possible for the firing pin to dent the primer? I have killer firing pin springs. My firing pins crush the primer before its little buddies, the case, powder and bullet know the primer has been crushed. Think about it; F. Guffey