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!