Casting Session, NOE 310-165-FN (30 XCB)

fiver

Well-Known Member
gas goes wherever it can.
around the case, along the bullet, ahead of the bullet, anywhere it can expand into it will.
if it didn't do that it would never move the bullet or expand the case.
 

Rick

Moderator
Staff member
Yep, equal pressure in all directions, that's why the primer doesn't seat as deeply after several firing, the web moves rearward. Plus the gas is much faster than the bullet so as soon as there is the slightest room between the cartridge case and the bullet gas will blow past the bullet. Gases and unburned powder will be the first thing out the muzzle.
 

Bret4207

At the casting bench in the sky. RIP Bret.
I think unless we're talking a very poor static fit the amount of anything but the gases themselves escaping in front of the bullet will be extremely small. In a case of very poor fit, yes, of course a great deal more gas can jet by the bullet and erode all sorts of alloy, lube, etc and cause all sorts of problems. But in a "tack driver" shooting lead it seems entirely counter intuitive to think a significant amount of lube precedes the bullet from which it came. The gases/fouling/atmosphere pushed out ahead of the bullet are something else.
 

L Ross

Well-Known Member
I think unless we're talking a very poor static fit the amount of anything but the gases themselves escaping in front of the bullet will be extremely small. In a case of very poor fit, yes, of course a great deal more gas can jet by the bullet and erode all sorts of alloy, lube, etc and cause all sorts of problems. But in a "tack driver" shooting lead it seems entirely counter intuitive to think a significant amount of lube precedes the bullet from which it came. The gases/fouling/atmosphere pushed out ahead of the bullet are something else.
Oh, but now that the Amigos have my thinking cap screwed on tighter, I am realizing that static fit is important but.....once the firing pin jams the case against the extractor or the shoulder, the primer pops, the bullets starts to move, inertia is being over come. The case neck releases its hold. The amount and intensity of gases being created and running pell mell in every possible direction. The case is stretched back, reseating the primer, the brass seals the chamber for a fraction of an instant before contracting.
Gas blows by the bullet, the alloy resists or alloys gas to blow by, the trailing side of the land groove widens more or less.
Now I have to understand, control, or accept the results of all of this. If my target loads generate X amount of gas and pressure, for X amount of time, what happens during the transition from static fit to dynamic fit?
Now start screwing around, asking my loads to produce more velocity, either to improve hunting performance or flatten my trajectory, and all of those variables need to be tweaked. Jacketed bullets seem to accept a wider range of variables and abuses, than traditional alloy bullets and lube. And Viola'! I now see the advantage of powder coating. Dog gone it, I have fought out the idea of PC with tenacity. I just didn't don't want to go there. But, now I see that may end up being the easiest solution to micro managing a herd of variable "cats". Trying to manipulate all of the little things that traditional cast bullet shooting brings to the party, and why one happy circumstance of load, accuracy, satisfaction, doesn't necessarily mean it will work when I start changing what I ask it to do.
Rather than tweaking my alloy, playing with my brass, manipulating my pressure curve, jam fitting, jumping, on and on, I can perhaps reap some of the benefits of both jacketed and home cast all by in effect making my own plastic jacketed, inexpensive, not subject to shortages, custom home made bullets.
 
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Rally

NC Minnesota
L Ross,
Good explanation, but doesn't the seal come before the stretch?
I'm resisting PC'ing, it makes sense, application seems easy enough, and reports are it works. I just don't need anymore bad habits! Same reason I haven't gotten into archery over the years.
 

Bret4207

At the casting bench in the sky. RIP Bret.
Back up to where the primer has lit off some of the powder, the gases are expanding, the pressure increases, the case swells and the neck opens. If the bullet is seated hard into the leade, then the pressure is going to rise until it starts moving. Is the pressure moving only forward against the bullet base? Of course not. It's going towards an area of lower pressure in a period measured in nano senconds I suppose. The pressure seeks an escape, so to speak, and the only place for it to go once the case has expanded fully is in between the bullets foresection (whatever shape that may be) and the grooves. Is there any lube for the pressure to carry with it there? No. So are we to believe that the gas, burning from the rear is moving in a linear direction or are we to believe the pressure rises more or less equally within the case? Until there is a area of lower pressure for the gases to occupy, (the grooves), the gases are busy swelling the case out, shoving the case back and so on. As the bullet starts to move the first part of the bullet to fill the groove seals that escape area. (Is there a reverse pressure wave created at that point?) The gases are not moving in a linear fashion along the sides of the bullet, at least not in my imagination. The gases are piled up against the throat area and all of it is trying to get into the groove space. There is only a tiny area for the rushing gases to accelerate to any degree and that's in between the nose and front of the first drive band. If there was lube there, then yes, I could see some being carried into the barrel ahead of the bullets first drive band or even, perhaps, the nose. If there isn't, where is the lube supposed to come from? If the bullet isn't hard seated, if the nose has to go a ways before it starts to engrave and seal, then my imaginary movie of this happening is still not seeing linear gas pressure back at the lube grooves, but up in front of the nose. Yes there is a pressure wall that moved as the intial powder started burning, but that wall (I picture a storm front) is relatively low pressure as it first moves across the body of the bullet as the case starts swelling and the neck opens. If anything, I would think the pressure is going to rapidly fall in the tiny time period as the neck opens, the lube in it's grooves starts to compress into any space available and the front of the pressure wave moves to the bore. Of course more powder is burning and pressure increasing, so maybe it's a wash in that respect. Once the bullet is moving and gets into the throat and leade, conventional wisdom says it sort of stops or slows at least and the pressure builds at a different rate until the bullet regains it's movement. Again, the pressure builds more or less equally, we have to say "more or less" because we can't measure inside the case, and the only place for it to move to is that area between the groove and first drive band. I can visualize a tiny bit of lube being thrown forward from the relatively sudden slowing of the bullet, but we're into that time/pressure/distance area again. Is there actually time for any lube to move in the period? I dunno. Is the lube capable of moving under the ambient pressure? I dunno. Once the first drive band is in the groove, given anything like decent fit and smooth barrel, we shouldn't have much, if any, escaping gases. At least that's what we aim for. So I'm back to how, when and where could any significant amount of lube get ahead of the bullet that is came from?

Let me say this- What I lay out is how I picture it. I believe, and I have no more proof than anyone else, that most of the lube that is deposited in our barrels gets there in the throat and first few inches of the barrel when the bullet has the most chance of being "plastic" and that some lube is forced against the barrel walls as the bullet compresses. I also think some is thrown against the barrel walls from acceleration. I think, again with no real proof, that a good deal of the lube that is lost off the bullet occurs as is exits the muzzle and the following gasses do have a chance to rush by as the bullet starts to slow. Some may be lost as the bullet spins it way to the target. It's all conjecture as I imagine things progressing. I won't ever put it in terms of "This is what happens..." because it's just a theory. Sometimes things are said that don't make sense to me. I tend to obsess a little I suppose, but as I said, it sure beats trying to figure women out.

There ya go. Worth every penny you paid for it. No disrespect to anyone, anywhere intended.
 
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fiver

Well-Known Member
if the case is gripping the chamber the stretch Is minimized or isolated to one section of the case.

think about the tests Parker done like shooting the 30-30 with no locking lugs.
as soon as he made the round more of a cylinder and less of a wedge the case grip increases and the stretching all but stopped.
I took his design out even further in my X57 rifle and do nothing more than fire form and neck size full pressure loads, I'm on 6 firings with no signs of chambering issues on some cases.
the downside is I can easily exceed 60-K with no real pressure signs [except exceeding 3,000 fps] so have to be very careful working up loads.
 

Bret4207

At the casting bench in the sky. RIP Bret.
Oh, but now that the Amigos have my thinking cap screwed on tighter, I am realizing that static fit is important but.....once the firing pin jams the case against the extractor or the shoulder, the primer pops, the bullets starts to move, inertia is being over come. The case neck releases its hold. The amount and intensity of gases being created and running pell mell in every possible direction. The case is stretched back, reseating the primer, the brass seals the chamber for a fraction of an instant before contracting. Stop there- the brass is going to remain blown out against the chamber walls from the instant the yield strength (for lack of the correct term) is hit until the pressure falls back down below that point. It may not be an instant in terms relative to the time it takes for the powder to burn and bullet to move up the barrel. It may be well past the time the bullet is halfway up the barrel or more, depending on powder burn rate.
Gas blows by the bullet, the alloy resists or alloys gas to blow by, the trailing side of the land groove widens more or less.
Now I have to understand, control, or accept the results of all of this. If my target loads generate X amount of gas and pressure, for X amount of time, what happens during the transition from static fit to dynamic fit?
 
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fiver

Well-Known Member
correct and is why in some gas operated guns you will see case stretching.
it isn't so much from the case stretch to fit the chamber but from the extractor pulling the case out of the chamber while the case walls are still gripping it.
many of those types of rifles are going to or have gone to chrome lining to help with that happening.
 

Bret4207

At the casting bench in the sky. RIP Bret.
if the case is gripping the chamber the stretch Is minimized or isolated to one section of the case.

think about the tests Parker done like shooting the 30-30 with no locking lugs.
as soon as he made the round more of a cylinder and less of a wedge the case grip increases and the stretching all but stopped.
I took his design out even further in my X57 rifle and do nothing more than fire form and neck size full pressure loads, I'm on 6 firings with no signs of chambering issues on some cases.
the downside is I can easily exceed 60-K with no real pressure signs [except exceeding 3,000 fps] so have to be very careful working up loads.
In my dream world where I build all the rifles I envision, I'd take a Savage 99 action and rebarrel it to 25/35 Ackley. With near parallel case walls back thrust should be minimal and the blown out case would let me approach 250-3000 velocity without fear of stressing an old square bolt 99. There's an awful lot of good stuff in his books.
 

L Ross

Well-Known Member
L Ross,
Good explanation, but doesn't the seal come before the stretch?
I'm resisting PC'ing, it makes sense, application seems easy enough, and reports are it works. I just don't need anymore bad habits! Same reason I haven't gotten into archery over the years.
Stretch make have been a poor choice of words. I am to big to fit inside the chamber for an eye witness report, but I think the case has to move back before it expands radially to grip the chamber walls. Anyone here help me out?
 

Rally

NC Minnesota
Rally, I just have a hard time buying into the theory, and it is only a theory, that any significant amount of lube can somehow preceed the bullet into the bore. Some seem to make the assumption the pressure is only directed forward, or something along those lines.

Bret,
I'm not sure there is a "Significant" amount of lube being carried forward by the gases bypassing the bullet, but I have to believe there is some being carried by the gases, because I picture my lube being in a near liquid state from pressure. I don't see where anyone in this thread has stated the pressure is only directed forward, most have stated in goes where it can/ path of least resistance/ void/ equal in all directions. I've just often wondered what percentage of the lube was carried forward of the bullet, and how exactly lube is distributed along the bullets path down the bore in a high pressure rifle loading. I'm thinking of a .30 cal bullet weighing 195 grs. (because I have the bullet recovered from my deer this year in my hand). A .45 cal. bullet found in a berm or bullet trap isn't a fair comparison in my mind with the pressure difference. Just food for thought. LOL
 

Rally

NC Minnesota
correct and is why in some gas operated guns you will see case stretching.
it isn't so much from the case stretch to fit the chamber but from the extractor pulling the case out of the chamber while the case walls are still gripping it.
many of those types of rifles are going to or have gone to chrome lining to help with that happening.

And also why belted mag cartridges show stretch marks/ ring, most prevalent just forward of the belt
 

Bret4207

At the casting bench in the sky. RIP Bret.
Bret,
I'm not sure there is a "Significant" amount of lube being carried forward by the gases bypassing the bullet, but I have to believe there is some being carried by the gases, because I picture my lube being in a near liquid state from pressure. I don't see where anyone in this thread has stated the pressure is only directed forward, most have stated in goes where it can/ path of least resistance/ void/ equal in all directions. I've just often wondered what percentage of the lube was carried forward of the bullet, and how exactly lube is distributed along the bullets path down the bore in a high pressure rifle loading. I'm thinking of a .30 cal bullet weighing 195 grs. (because I have the bullet recovered from my deer this year in my hand). A .45 cal. bullet found in a berm or bullet trap isn't a fair comparison in my mind with the pressure difference. Just food for thought. LOL

Ya gotta go back a couple pages to get to the lube being blasted out the muzzle ahead of the bullet theory. I specifically used the term
"significant" because the theory has been put forth, or so it seems to me, that lube is commonly "blown forward" somehow. How? Theres nothing I can see that can take the static lube, somehow "get behind it" and push it into motion. If this was the case, why would any lube remain in any lube groove? Shouldn't it all be pushed out of the grooves and along the ID of the neck? This gets us to your idea that the lube is turned from a solid, or at least a paste in a real soft lube, to "liquid" from the pressure. When we say "pressure" we also mean heat, and thats beyond the heat of the burning powder, which may not even reach the lubed area before the bore is sealed. Even under tremendous pressure it takes time for heat to transfer to a substance and bring it to the melting point, or so I'm lead to believe. It takes time for a fuel to ignite under compression and burn which is why timing an engine isn't a simple thing at all. It's why the theory that "bullets melt from the burning powder and that causes leading" doesn't work out. I would think the same basic idea of pressure/time would apply to lube in a case. I get stuck wondering how long that takes, if the gases are capable of somehow sucking some of that lube up out of the groove as they pass by in some weird venturi effect or of somehow being directed down into the lube to "push" it out as though you were spraying it with a hose (extremely doubtful since the pressure is surrounding the bullet on all sides) or if maybe there's a force no one has mentioned that could move the lube that all that pressure should be forcing into the grooves rather than out of them. That gets me to the idea that maybe the pressure does push the lube out of the grooves, but that makes no sense since the pressure is the same around the bullet, there's no lower pressure area for the lube to move to. If the lube was that liquid and was being blown around, why would we find much of any on a fired round and why wouldn't the area between the neck and throat be packed with lube? So that's why I use the term significant. Cleaning stalls takes time and this is the stuff I think about!

Again, I'm not saying I'm right. I'm probably dead wrong. I just haven't seen anything that makes sense for some of the other theories that state lube gets blown down the bore ahead of the bullet in any amount large enough to be able to tell it actually happens. Unless the nose is covered in lube near the nose/groove interface space, I can't figure out how it can happen. But I'm just hick from the sticks, so I'm likely missing something entirely obvious to someone else.
 

Bret4207

At the casting bench in the sky. RIP Bret.
Stretch make have been a poor choice of words. I am to big to fit inside the chamber for an eye witness report, but I think the case has to move back before it expands radially to grip the chamber walls. Anyone here help me out?

The movie playing in my mind shows the case starting to move back as the case walls and neck start to expand and the crimp, if there is one, starts to give. I imagine when the case head is fully back against the bolt/breech face the case expands more fully and as the action stretches/slack is taken up/expands from the still rising pressure the brass continues to expand a bit more to it's maximum. It should remain at it's max until the pressure drops to a certain point and then spring back begins. At least in the B movie in my head that's how it plays out. Case shape is going to play a big part in how much back thrust there is. A wedge shaped 25/35 or 8mm Lebel is going to exert more rearward pressure because (I think) the pressure pushing the case rearward is also pushing the case walls against the wedge shaped chamber. Of course all this is happening much faster than your standard 2 shakes of a lambs tail or blink of an eye.

I would also bet that a properly chambered and headspaced gun is going to see the case walls grip quicker and more effectively than the Bubba's Gun Schmittin' and Bait Shop special. Isn't that along the lines of why we neck size rather than full length resize?
 
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fiver

Well-Known Member
gotta remember that a primer is pushed out and then re-seated again.
sometimes fully, some times not, and sometimes it's pushed out and malformed and then re-seated.
[top hat]
it might only be pushed out .002 or so, or just flush to the case head if you've really got your cases fit tight.
 

Ian

Notorious member
Wow, we created a monster!

Here's one I've been saving for a few years now and while it doesn't support my case for lube blowout before obturation of the bore it IS a pertinent data point. This is from my one and so far only accidental squib load back when I was furiously attempting every load, alloy, lube, and bullet combination I could think of to try and get some sort of acceptable accuracy from my DI-45 carbine. The lube is SL-68.1 (Lamar had a small sample of the stuff at one time and knows it's on the soft side). Absolutely zero lube loss. The primer sooted ONLY the base of the bullet. It lodged in the throat (this chamber has a nice, long, gradual throat) and I tapped it out with a BP ramrod.

20200228_222923_20200228223055621.jpg

I have no idea what actually hapoens with a 15-20KPSI charge of powder behind it peaking at right about the point that this bullet stopped, but with only a orimer this is what happened, fwiw.