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Does the bullet slide out of the neck or does the neck open to release it?

I never, or possibly very rarely, ever see the complete absence of blow by before bullet exit. I do assume the bullet seals the barrel, and a video where gas is escaping AS the bullets exits would point to some serious inaccuracy questions.

If we view a cartridge and its neck as little different than a plastic straw in how it behaves under pressure, then even though a solid object may fit tightly in the end of it, nominally, once highly pressurized, the straw will expand like a balloon taking the shape of its container, even, and especially if the bullet were not allowed to move at all - in which case the gas would expand the neck and leak out around the bullet.

If that were to happen, it will expand from the back end of the bullet toward the front, not all at once, and certainly not from the front of the neck to the back, just like those animal tube balloons inflate from the source of pressure, forward. As a matter of degree, I think this is always happening to a greater or lesser extent.

Of course the bullet is never totally held in place, and the question is whether it can be jammed into the leade more easily than the neck can be expanded. It’s easily imaginable that on “some neck with some jammed bullet”, the bullet could move simultaneously with the neck expansion like a zipper unzipping, under pressure, but this may be a coincidence, rather than opening and “releasing” the bullet being a “causal” happening.

With no tension and little barrel resistance, then a thick neck might keep its shape until peak pressure, when that neck and the whole case expands and snaps back. If it had not expanded yet, then it might expand from “front to back” (the bullet is gone) as peak pressure - by definition - pushes dirty gas backwards, staining the exterior of brass with unsealed necks 1/3 of an inch down. We know peak pressure is toward mid barrel, not in the case, and this is clearly apparent to us in that rifle brass is only hot to the touch if peak-pressure-temperature gas is redirected into contact with brass, in the ejection cycle.
 
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If people test things, stuff gets a lot clearer.

While cutting the grass today I was wondering if somebody could make a "chamber stub" for lack of a better term. What I mean is to machine a chamber in a barrel and then cut it off at the end of the neck so the case neck is flush with the end of the stub and let the bullet stick out.

With a close up shot with a high speed camera we might be able to see clearly what happens with the initial bullet and case neck movement. It might be interesting to see what velocity is attained with zero barrel length as well.
 
While cutting the grass today I was wondering if somebody could make a "chamber stub" for lack of a better term. What I mean is to machine a chamber in a barrel and then cut it off at the end of the neck so the case neck is flush with the end of the stub and let the bullet stick out.

With a close up shot with a high speed camera we might be able to see clearly what happens with the initial bullet and case neck movement. It might be interesting to see what velocity is attained with zero barrel length as well.
I've shot 22PPC rounds in a 6PPC chamber. There is some pressure generated but not much. Bullets land 30-60 yds down range. Think sling shot velocities. SAAMI has a video of all kinds of ammunition being cooked off in a fire. Almost no pressure generated. A fire crew could fight the fire and not be in danger.
 
IIRC from a ballistics manual I read quite a few years ago, the bullet begins to move forward when the case pressure reaches between 2-10,000 psi. This is well before peak pressure of 40-60,000 psi is achieved. I believe this is called "shot-start pressure".
 
Does the pressure/push from primer ignition pushing powder forward push the bullet out because of pushing the powder plug forward during initial ignition ?? Or does that push from the powder plug expand the neck as well??
 
Don't know the answer, however, in our research on fast reacting high pressure transducers, we contacted PCB Piezotronics several months back. They supply equipment, mainly transducers, to OHLER for SAAMI spec testing. They mentioned the peak pressure spike in the brass and a secondary pressure spike as the bullet travels down the barrel. His remarks were centered around the military testing they have witnessed. One gentleman remarked that we deal with just over a millisecond of barrel time, but the bullet leaves the brass in probably nanoseconds. Seems that it would be virtually simultaneous.
 
You bet. With our .085 neck length .30 WolfPup cases....the loads needed to be up there. Attempts with slower burn rate powders always resulted in gas leakage around the necks and past the shoulder/body junction.

It wasn't so much the actual pressure but more the powder burning rate and what I term the 'rise time'....for lack of a better description.

Good shootin' :) -Al
Does "impact duration" (also know as IMPULSE in physics and engineering science), better describe your term of "rise time"?????
 
I never, or possibly very rarely, ever see the complete absence of blow by before bullet exit. I do assume the bullet seals the barrel, and a video where gas is escaping AS the bullets exits would point to some serious inaccuracy questions.

If we view a cartridge and its neck as little different than a plastic straw in how it behaves under pressure, then even though a solid object may fit tightly in the end of it, nominally, once highly pressurized, the straw will expand like a balloon taking the shape of its container, even, and especially if the bullet were not allowed to move at all - in which case the gas would expand the neck and leak out around the bullet.

If that were to happen, it will expand from the back end of the bullet toward the front, not all at once, and certainly not from the front of the neck to the back, just like those animal tube balloons inflate from the source of pressure, forward. As a matter of degree, I think this is always happening to a greater or lesser extent.

Of course the bullet is never totally held in place, and the question is whether it can be jammed into the leade more easily than the neck can be expanded. It’s easily imaginable that on “some neck with some jammed bullet”, the bullet could move simultaneously with the neck expansion like a zipper unzipping, under pressure, but this may be a coincidence, rather than opening and “releasing” the bullet being a “causal” happening.

With no tension and little barrel resistance, then a thick neck might keep its shape until peak pressure, when that neck and the whole case expands and snaps back. If it had not expanded yet, then it might expand from “front to back” (the bullet is gone) as peak pressure - by definition - pushes dirty gas backwards, staining the exterior of brass with unsealed necks 1/3 of an inch down. We know peak pressure is toward mid barrel, not in the case, and this is clearly apparent to us in that rifle brass is only hot to the touch if peak-pressure-temperature gas is redirected into contact with brass, in the ejection cycle.

In the design of the rifling, a safety factor (and liability of the barrel maker) is built into the design, the tooling mainly, to allow clearance for oversized (diameter) factory bullets and is like thread design (fasteners)!!! Clearance, or pressure relief design, is set for 2 reasons!!
1. Over pressure spikes from a sealed bullet in the barrel contacting fouling in the major diameter of the rifling!!!
2. The reduction of friction (bullet bearing surface not contacting the major diameter of the rifling cut) to eliminate pressure spikes and maximize bullet acceleration down the barrel!!

Now, the evidence of this designed over relief cut of the major diameter can be found in 2 ways:
1. In examining the terminated bullet, very little or no barrel scratch marks on the non rifled bearing surfaces of the bullet!!
2. Bore scoping and examining where the majority of copper fouling occurs in a few shots fired through that barrel!! Very little, if any is observed on the major diameter!! If some fouling occurs in this diameter, there is a problem in bullet/rifling alignment or bullet diameter!! But, examining a really copper fouled barrel, there will be copper residue on the major diameter due to flowing of the copper from excessive build up on the rifling!!!

The pressure velocity potential of the hot gases behind the bullet is way higher than the bullets muzzle velocity itself!! The faster moving escaping gases through the relief design of the bullet/barrel mixes with the accelerating pressure wave of air in front of the bullet!!! This pressure wave of now increasing hot gasses and compressing air is called a gradient (a velocity vector derived from the pressure using vector calculus)!! The video clip shows that gradient or pressure wave out in front of the bullet!!!
 
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I've shot 22PPC rounds in a 6PPC chamber. There is some pressure generated but not much. Bullets land 30-60 yds down range. Think sling shot velocities. SAAMI has a video of all kinds of ammunition being cooked off in a fire. Almost no pressure generated. A fire crew could fight the fire and not be in danger.

When you have done that, is the neck fire-formed and oversized? I’m supposing so since a paper wad will fire form the shoulder.
 
"Does the bullet slide out of the neck or does the neck open to release it?"

Yes.....you're welcome.:p:p


What are the chances this lingering question will be rattling around upstairs in a couple weeks, while on the line warding off them Bayou boys in the next V2 finale? (We call these “leading questions”, lol).
 
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IIRC from a ballistics manual I read quite a few years ago, the bullet begins to move forward when the case pressure reaches between 2-10,000 psi. This is well before peak pressure of 40-60,000 psi is achieved. I believe this is called "shot-start pressure".
Strange, because after this thread started I actually measured the force required to seat a bullet into a case,
With a spring pressure gauge
The vertical force required was only 50 lbs - (actual force to push bullet into neck)
Would seem logical the force required to spit the bullet back out would also only be 50 lbs.
---Until it reached the rifling
---This was a 22BR case with light neck tension
I know other cases such as 300 WM have much more neck tension and seating force required could be
10x this.
But still does not come close to 2k-10k PSI
 
Would seem logical the force required to spit the bullet back out would also only be 50 lbs.
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Liquids are not compressible, Solids can be compressed. But by your
definition, it does bring up another point. Although the rifle powder
is a solid, it's broken down into a particulate, then can be compressed
more easily, such as a compressed load.......Too many worms in this can,
but a good conversation anyways......
If I read Wild Bill correctly I think what he is saying is
"90% of the case is already filled with a solid, the remainder of the volume is acting as a liquid"
The solid is not any more compressible than the rest of the liquid
the powder is compressible when there is simply atmosphere in between the kernels until it's lit off.
Once lit off and the gas pressure rises to the point it acts as a liquid, and the granules do not compress in between or against one another.
It's more like filling a Jar with marbles, then topping the jar off with water
the space in between the marbles is filled with water - nothing in the jar is compressible at that point
 

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