When does the case neck expand?

JerrySharrett

JerrySharrett

Senile Member
Cabin fever question-when does the case neck expand?

-Upon powder ignition, does the case neck expand then release the bullet..

-or does the pressure of ignition of the powder push the bullet out then the some 50KPSI expand the case neck?

Bringing up the question is it more important to have a small amount of neck-to-chamber clearance which better aligns the bullet-to-freebore.
or is it more important to have good release of the bullet with more neck-to-chamber clearance?



....or does it matter??

(yes, I'm turning brass)


..
 
Another possibility is when the primer ignites. What happens if you fire a round with a live primer, but the case is filled with an inert substance like cream of wheat?
 
James Lederer said:
Another possibility is when the primer ignites. What happens if you fire a round with a live primer, but the case is filled with an inert substance like cream of wheat?
Click to expand...

With average neck tension the bullet doesn't move, at least the few I forgot to drop powder in!


.
 
Jerry-tell me if my sequence is correct

Tell me if my sequence is incorrect-
1- static situation: Loaded round with either factory or substantial neck tension.
2- load round in chamber;
3- trigger is pulled. Ignition is started by the primer and the powder column is ignited. The bullet is held by neck tension. Pressure is felt inside the case, starting its expansion.
4- Case internal pressure overcomes neck tension, releasing the projectile. Case is forced outwards backwards by expanding gasses, sealing the chamber.
5- Powder continues its combustion, pushing the projectile towards the target.
6- When pressure is reduced by the increase of the volume of the gas chamber (case volume + barrel volume), case metal initiates springback, where brass elasticity allows case to allow case extraction.

With this scenario, the case neck only releases the projectile once the case expands enough to allow it.
So my answer to the question is:
yes to the following:
quote-or does the pressure of ignition of the powder push the bullet out when the some 50KPSI expand the case neck?endquote

Cheers,

Phil Fortin aka tazzman
 
not quite correct...
neck releases bullet which engages the lands and allows pressure to reach a point where the bullet is forced
into the bbl.
it is some where between bullet release and bullet movement past the throat that max pressure is reached...which is where max
case expansion occurs.
IMHO

tazzman said:
Tell me if my sequence is incorrect-
1- static situation: Loaded round with either factory or substantial neck tension.
2- load round in chamber;
3- trigger is pulled. Ignition is started by the primer and the powder column is ignited. The bullet is held by neck tension. Pressure is felt inside the case, starting its expansion.
4- Case internal pressure overcomes neck tension, releasing the projectile. Case is forced outwards backwards by expanding gasses, sealing the chamber.
5- Powder continues its combustion, pushing the projectile towards the target.
6- When pressure is reduced by the increase of the volume of the gas chamber (case volume + barrel volume), case metal initiates springback, where brass elasticity allows case to allow case extraction.

With this scenario, the case neck only releases the projectile once the case expands enough to allow it.
So my answer to the question is:
yes to the following:
quote-or does the pressure of ignition of the powder push the bullet out when the some 50KPSI expand the case neck?endquote

Cheers,

Phil Fortin aka tazzman
Click to expand...
 
FBecigneul said:
It doesn't do anything until you extract it and measure it after it cools. Anything before that is pure speculation.
When I was in the Army (US), we used an ignipressoexpometer to resolve the issue.
Plus it happens so fast you can't prove it.
Click to expand...

Francis, when you were in the Army (US) they did not have case necks (round balls didn't need them).

Plus, serial numbers were still just double digits.

Iginiressopomrter?? That have to do with the Internet?


.
 
The bullet has 'way more mass and inertia than the case neck, so when pressure is applied to both, and the pressure is high enough to overcome the sliding friction between the bullet and the neck (for a 0.308" bullet in a 0.328" OD neck, this occurs at no more than about 4k psi, even if the neck is work-hardened), the neck accelerates radially faster than the bullet accelerates axially. So the bullet has started to move, but the neck expands away from the bullet before the bullet is completely out of the neck. Just my calculations, but I would be surprised if actual measurements showed anything different.

Keith
 
mks said:
The bullet has 'way more mass and inertia than the case neck, so when pressure is applied to both, and the pressure is high enough to overcome the sliding friction between the bullet and the neck (for a 0.308" bullet in a 0.328" OD neck, this occurs at no more than about 4k psi, even if the neck is work-hardened), the neck accelerates radially faster than the bullet accelerates axially. So the bullet has started to move, but the neck expands away from the bullet before the bullet is completely out of the neck. Just my calculations, but I would be surprised if actual measurements showed anything different.

Keith
Click to expand...


Thanks Keith

Your explanation sheds some light on an area I've always wondered about. :)

I sure enjoy your posts. There are those of us out here that hang on your every word.

Thanks again for sharing.

Gene Beggs
 
mks said:
The bullet has 'way more mass and inertia than the case neck, so when pressure is applied to both, and the pressure is high enough to overcome the sliding friction between the bullet and the neck (for a 0.308" bullet in a 0.328" OD neck, this occurs at no more than about 4k psi, even if the neck is work-hardened), the neck accelerates radially faster than the bullet accelerates axially. So the bullet has started to move, but the neck expands away from the bullet before the bullet is completely out of the neck. Just my calculations, but I would be surprised if actual measurements showed anything different.

Keith
Click to expand...

Outside of this discussion,I understand mass and I understand inertia. Inertia is the ability of mass to STAY in motion is it not? What does inertia have to do with mass that is only traveling 0.0005"?

I can agree that neck expansion takes place as a "rolling" motion. I.e. The neck expands, not all at once, but behind the bullet as it exits the case neck....whoa...is that the answer to my question?


..


.
 
Well...the black on the case neck increases with the neck clearance. It also increases with a lighter load. What I don't understand is why that black "dust" stops on the case neck rather than continuing onto the entire case. Something happens there and it happens rather suddenly.
 
JerrySharrett said:
Outside of this discussion,I understand mass and I understand inertia. Inertia is the ability of mass to STAY in motion is it not? What does inertia have to do with mass that is only traveling 0.0005"?

I can agree that neck expansion takes place as a "rolling" motion. I.e. The neck expands, not all at once, but behind the bullet as it exits the case neck....whoa...is that the answer to my question?


..


.
Click to expand...

Jerry,
Inertia makes it difficult to speed up or slow down the object compared to whatever velocity it currently has, including zero.

Right, the neck expansion rolls forward. The pressure opens the gap between the bullet from the shoulder toward the mouth, but the wave of neck expansion is complete before the bullet exits.

Keith
 
Wilbur said:
Well...the black on the case neck increases with the neck clearance. It also increases with a lighter load. What I don't understand is why that black "dust" stops on the case neck rather than continuing onto the entire case. Something happens there and it happens rather suddenly.
Click to expand...

The smoking stops at the neck/shoulder intersection probably because the shoulder is jammed?? What mystifies me is the dipping pattern of blacking on the case neck. two dips for a 2 lug bolt and 3 dips for a 3 lug bolt??

.
 
mks said:
Jerry,
Inertia makes it difficult to speed up or slow down the object compared to whatever velocity it currently has, including zero.

Right, the neck expansion rolls forward. The pressure opens the gap between the bullet from the shoulder toward the mouth, but the wave of neck expansion is complete before the bullet exits.

Keith
Click to expand...

Kieth, So you feel the neck expansion actually gets ahead of the bullet base at some point?

CCBW, lets send HFV in the chamber with a GOPro camera. Then we will know for sure.

.
 
CMaier said:
not quite correct...
neck releases bullet which engages the lands and allows pressure to reach a point where the bullet is forced
into the bbl.
it is some where between bullet release and bullet movement past the throat that max pressure is reached...which is where max
case expansion occurs.
IMHO
Click to expand...
Thanks CMaier, probably had a brain fart while keying the response. After reading the responses, it seems that there is more to it than I first thought.
 
JerrySharrett said:
The smoking stops at the neck/shoulder intersection probably because the shoulder is jammed?? What mystifies me is the dipping pattern of blacking on the case neck. two dips for a 2 lug bolt and 3 dips for a 3 lug bolt??

.
Click to expand...

I would also like to know the cause of the black dips, my two lug panda always have 3 dips?
 
not quite true part II,
It takes a few pounds of pressure to move the bullet out of the neck,( ever pull a bullet ??),
it takes aprox 40kpsi to deform brass. that pressure is not seen till
the bullet hits the throat and slows down and pressure builds from combustion.
 
CMaier said:
not quite true part II,
It takes a few pounds of pressure to move the bullet out of the neck,( ever pull a bullet ??),
it takes aprox 40kpsi to deform brass. that pressure is not seen till
the bullet hits the throat and slows down and pressure builds from combustion.
Click to expand...

HOley KOWW.....I'm now depressed I came on for a minute to browse......

Please Keith?

Pretty soon we'll have more exspurts opining as how HyDroxyGen Boride reduces friction which drops startup pressures and ......

I Know..... lotsa' these innernet heroes really got it going, on a dozen "shooting forums" but,

for any of you'se casually reading who're too lazy to TEST this stuff, please take the time to read some stuff from people who know whereof they speak ;) before haring off down the road most traveled.... it's DAN'rous down that road! (Read the political posts)

Back before this magical innernet thingie we'd have to keep our library cards up, JUST so's we could learn about stuff

It still works

http://www.amazon.com/Bullets-Fligh...qid=1449387874&sr=1-1&keywords=bullets+flight

http://www.amazon.com/Rifle-Accuracy-Facts-Harold-Vaughn/dp/1931220077

http://www.amazon.com/Designing-For...319&sr=1-2&keywords=forming+custom+cartridges

I can't currently come up with any other works by people who do their own stuff, the new books I own all rely on opinion instead of testing too.....but let me assure you, these will suffice :) These guys knew what they were doing, not what they'd learned from others' books. People who write books from other people's books bore me.


Or, another option, THINK?? We don't need cameras, we can organize TEST REGIMES and prove what's going on, or we can THINK of other instances.

CMaier, where do you GET this stuff??? Just egg'Zackly how does a shottygun build up to pressure? (I wouldn't jump on it but you treat opinions as if they were facts)

A revolver??

And what about all the brass that's been wrecked fireforming WITHOUT A BULLET?

I build charts and test expansion/sealing rates using a fake action and a hunk of cold-rolled with a hole bored thru it......it's called 'fixturing'.....it's how you test stuff hundreds and thousands of times without wasting expensive barrels in this pertickler case but the concept is useful for all sorts of things......


I'll go away now,

Sorry Wilbur




Ohhh, and to all ALL Y'all who aren't going to read anywhere else NOR test?????

read mks

then read him again

then print it off for later

seriously
 
al, ,
You have confused yourself.
This was not about shotguns nor straight walled pistols cases.
Go read the original question.

Apply my answers to HIGH PRESSURE CENTER FIRE BOTTLE NECK RIFLES CASES.
 
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