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

[AlNyhus]

Stan Ware and I learned a lot with our .085 neck length .30 WolfPups. Necks absolutely expand first. -Al

 

[Wild Bill IV]

Saw this video and found it pretty interesting. I know its facebook so if anyone can post a direct link that would help.

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That is easy question to solve by using physics!! The neck will not see pressure as the bullet is blocking the pressure!! FORCE = PRESSURE x AREA!! If the bullet is blocking the area, there is no force!! The force on the bullet base (area exposed to the pressure) forces the bullet out of the neck!! As the bullet moves forward, more neck area is exposed!! The neck is roll formed outward as more neck area is exposed!! Now, some are going to say the neck will be forces to open between the bullet and the neck region!! Once again, that area is so small compared to the area of the base of the bullet and will see much, much less Force!!! This is all engineered in the mechanics of interior ballistics!!!!

I can ask one question and the case is solved!! IF THE NECK OPENS UP FIRST, HOW DO YOU GET BLOW BY RESIDUE ON THE OUTSIDE OF THE NECK AND SHOULDER?????

 

[STS]

I did a test once where I installed a short piece of chambered barrel in my old RCBS Rockchucker press. Made a punch to fit in the shell holder. It took an unbelievable amount of force to push a 6.5 bullet into the barrel. So much force was required I had to lube the barrel for each bullet to continue the test. Just a SWAG but I'd say it takes maybe 50-75 times more force to push a bullet into the barrel than running an expander mandrel into the neck.
My vote is the neck expands first.

Good illustration. There is no way that a primer could generate enough force to push THAT bullet into THAT barrel. BUT, I have seen bullets pushed into the rifling by the energy exerted by a primer alone. So, bearing in mind the above two examples, I conclude that the question that Alex posed, is not an either/or situation where it is neck first, or bullet first, 100 percent of the time. It would seem the evidence points towards some barrel, bullet, primer and powder combinations being able to push the bullet into the rifling before the powder burn happens, and some combos incapable of doing that. One combo moves the bullet first, the other can't move the bullet, so the pressure builds, and opens the neck first.

 

[Wild Bill IV]

Moving deeper into the internal ballistics mechanics involves Rocket Science!! If you have watched rocket launches, there is an Hour Glass effect following beneath the engines!! The engines have double elliptical bells! This shape forces the hot gases and heat to the focal point of the elliptical shape!! A study in Analytical Geometry defines where the focal point is due to its shape!! This is called a singularly point where all the mass and energy converge!! All the engines are rotated to a singularly!! Thus, the thrust pushes against this singularity of very high, almost infinite mass density and propels the rocket forward using Newton's Law of Action/Reaction Forces!!

If you look at cross sections of bottle neck cases, the interior shape towards the base is also an elliptical shape, and has a focal point directly forward of the flash hole and behind the neck or base of a full seated bullet!! This is why seating depth is so critical!!! All the pressure being directed to the case base is reflected to the singularity point and redirects the pressure and mass straight forward and not outward!! This force pushed the bullet forward and very little pressure is pushing the neck outward!!! Therefore, due to turbulent flow, hot gases can now flow between the chamber and the outside of the neck and shoulder regions leaving behind residue!! As the singularity point losses mass and energy as the bullet moves forward, the pressure now is redirected outward more and forces the neck against the chamber!!!

ROCKET SCIENCE!!!

 

[Edd]

I can ask one question and the case is solved!! IF THE NECK OPENS UP FIRST, HOW DO YOU GET BLOW BY RESIDUE ON THE OUTSIDE OF THE NECK AND SHOULDER?????

The gas leaks between the bullet and case neck and flows around the case neck into the chamber. As the pressure and gas volume increase the case neck is fully expanded and the bullet is pushed into the barrel.

 

[Wild Bill IV]

The gas leaks between the bullet and case neck and flows around the case neck into the chamber. As the pressure and gas volume increase the case neck is fully expanded and the bullet is pushed into the barrel.

So you're saying the bullet magically hangs in space and gravity does not effect it???

Read my reply directly above your reply!!! The answer is there!! I've studied old Military interior ballistic reports from some of the old military testing grounds and ballistic labs that were being shut down in the early 70s to cut defence spending and consolidate at the Aberdeen Military Testing Grounds and Ballistic Lab Facilities!! Who knows more about Ballistics than the Military???? I have studied Newtonian Physics (also called Mechanic for Engineers), Thermodynamics, Calculus, Dif EQ, Chemistry, Physical Chem, and fundamentals in Hydrodynamics, and Quantum Mechanics!!! All applied sciences used in Interior Ballistics!!!

 

[dellet]

I’m still trying to figure out the question, “leaving the neck” sounds like the bullet is completely forward of the case, not simply moving forward into the lands.

What happens if the bearing surface of the bullet is shorter than the distance from the case mouth to the lands?
Where the bullet can be completely out of the case, free floating in the throat, before engaging the lands and grooves?

Shooting low pressure loads may also change the answer

 

[AlNyhus]

Shooting low pressure loads may also change the answer

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

 

[Wild Bill IV]

ON THIS DEBATE, EVERYBODY SEEMS TO FORGET ABOUT THE UNBURNT POWDER THAT IS CRAMMED FORWARD, AROUND A COUPLE OF MILLISECONDS, LEFT AND LOW ON THE PRESSURE CURVE!!!

Look at some physical properties that apply in this debate!!! Gases are highly compressible, liquids are slightly compressible, and solids are not compressible!!

Take a brown glass empty beer bottle and smack the mouth really hard, but firm, open flat palm!! Nothing happens because the air is a gas and it can take the pressure spike of the blow since it can be compressed!! Now, fill that bottle with water, and pop it hard and firmly with your open flat palm, the glass bottom of the bottle falls out!!! Hydrostatic Pressure at work directing the pressure spike straight down to the bottles base and not outward pressure which would break the thinner sides and neck!!! Same thing happens in bullets base just like the water filled bottle base!!! The bullet is already forced fully into the lands by hydrostatic pressure (of the hot gases and unburnt powder) before the outward pressure acts on the neck!!! Thus, turbulent flow deposits a smooth liquid like residue on the outside of the neck and possibly the shoulder before the outward pressure forces the neck against the chamber!! This is why hydrodynamics is involved in interior ballistics and their equations! This is the thrust against the forward burning column of propellant!! ROCKET SCIENCE!!

If you don't believe hydrodynamics is happening, then explain to me why the residue has smooth and even regions in the inside of the case and around the neck!! Burning powder in open air leaves a grainy or scaly texture on a smooth surface where it turns into a gas and not a liquid within the confines of the case and chamber where pressure spikes exponentially!!

The 2 phase (gas, solid) flow interior ballistic model, used in reloading software (INPUT powder type, powder weight, case cap., bullet weight, barrel length, twist, etc, with pressure and velocity OUTPUT), acts as a fluid!! Simply stated!!! The crushed powder blocks the hot, high pressure gases from going between the bullet and the neck as so many have stated above!!!

 

[dellet]

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

If I’m following you, rise time, also effects rate of acceleration. In a car that would be the 0-60 time.

I ran across this testing a bullet that was an expanding monolithic with an aluminum tip. The issue showed with the bullet coming apart at the muzzle at 2700 fps in a 1/9 twist, while remaining intact at 2800 fps in a 1/7.

What was determined was that the acceleration in the 1/9 do to using a much faster powder combined with the weight of the aluminum tip, initiated the expansion of the bullet as it accelerated in the first few inches of barrel. Peak pressure was essentially the same, only difference was the time from primer ignition to peak pressure.

The Wolf Pup certainly changed my thoughts on neck tension, seated depth and conventional thinking. One of those things that really influences someone to think and test outside the box.

 

[whatsupdoc]

I believe that it is a combination of both, as the pressure builds the acceleration of the gas far exceeds that of the projectile, the gas pressure forces the brass just before the bullet to stretch outward opening a path for more gas to get between the bullet and the case causing the case neck to stretch enough to release some pressure on the bullet.

The bullet is moving forward during this process so the bullet is not just released
by neck its a combination of both.

 

[Fuj]

EVERYBODY SEEMS TO FORGET ABOUT THE UNBURNT POWDER THAT IS CRAMMED FORWARD IN THE CASE ON THIS OPS DEBATE!!!!

Look at some physical properties that apply in this debate!!! Gases are highly compressible, liquids are slightly compressible, and solids are not compressible!!

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......

 

[Wild Bill IV]

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......

The compression properties are about cramming in more phase elements into a fixed container! If you take a closed container of gas, you can cram more in, but the pressure will increase proportionally!! With a liquid, like water, you can get a little more in, but the pressure will spike exponentially!!! If that container is fill with say solid lead, trying to add more, the pressure would have to be extremely, almost infinite to add a little!!! This is based on Thermodynamic!! Yes, adding more air increases the temperature proportionally!!! Adding more liquid spikes the temperature exponentially!! But adding more solid, to that already full volume, the temperature would be enormous!!!!

These properties define the basics of pneumatic (gases) and hydraulic (liquids) mechanics!!!

I was using Thermo properties for my statement above!! I'm sorry for not stating that fact in my previous reply!!!

An accumulation of solid particles can be slightly compressed!! But you are getting to my point with your analogy!!! Think of that gas and those broken and fragmented grains flowing!! They would move like cement but with a density slightly greater than water!!! This is where Hydrodynamics comes into play!!! Think about the power of fast moving flood water ripping up trees and knocking out bridges!!! Same thing is happening with the bullet/case in firearms with accelerating pressure and flow!!

 

[Alex Wheeler]

Stan Ware and I learned a lot with our .085 neck length .30 WolfPups. Necks absolutely expand first. -Al

Thats always been my opinion. On target the actual neck tension (interference fit) always showed as more important than seating force (friction) in my tests and others. I do remember a friend that had a rifle with a very long throat and the bullet was seated way out. It was also a slower powder as well. That bullet did slide out. We know that because the necks didnt expand. Pressure equalized on the outside of the necks.

 

[DaWhit]

I am coming at this from years of experimenting with loads in smokeless muzzleloaders.
As already referenced, full forming a bullet, which is running a bullet through an adjustable die with a section of your barrel drop to cut the lands and grooves into the bullet as well as sizing the diameter of the bullet takes considerable force. Much more force than what it takes to seat a bullet in a case. The caliber and bullet makeup makes a difference as well. Heavy jacketed or mono bullets are harder to size than thin jacketed bullets.
With the help of another guy with pressure trace equipment, we did a lot of experimenting with duplex loads and slip fit bullets, which is a sized bullet that rides on the lands as opposed to a full formed bullet. The ignition system was less than perfect compared to a fully enclosed cartridge case with the unfilled grooves to allow pressure to leak by. In order to get more velocity and stay in a pressure friendly area, you needed a faster burning powder layered under a slower burning powder to get the efficiency with light for caliber bullets. Mixing the two powders worked also but you had to change the ratio of the duplex to achieve the same velocity, the mix would yield lower pressure and velocity as opposed to a layered duplex. Bullet composition also factored into the equation.
When we got into the .375 caliber, a very fast burning booster that worked fine in a .45, would produce a camel backed pressure wave at peak pressure. Peak pressure would be achieved then a slight drop in pressure, followed by another pressure increase as the slower burning powder took over. Changing to a slower burning booster would produce a nice smooth pressure hump.

All that to say, I believe it is a combination. I believe the bullet moves first on ignition, then as the powder burns and the bullet gets drove into the lands, pressure rises and swells the case to seal off the neck.

I am just a dumb redneck hillbilly with far less intelligence than a lot of people who post here, but that is my take on it and could be completely wrong.
Good interesting topic.

 

[Wild Bill IV]

Thats always been my opinion. On target the actual neck tension (interference fit) always showed as more important than seating force (friction) in my tests and others. I do remember a friend that had a rifle with a very long throat and the bullet was seated way out. It was also a slower powder as well. That bullet did slide out. We know that because the necks didnt expand. Pressure equalized on the outside of the necks.

Was the residue outside of the neck as dirt as the inside?
Did it have a fine spray paint effect?
I would like too know if my research is taking me in the right direction with these questions!!!!
By the way, your words in statements are sounding more like a scientist compared to replies from the past!! Inference fit falls into Engineering "Class Fit"!!!

ELON MUSK: PHYSICS IS BASED ON PRINCIPLES AND NOT ANALOGIES!!

 

[Edd]

So you're saying the bullet magically hangs in space and gravity does not effect it???

Yes.

 

[243winxb]

If this neck expanded? When?

 

[AlNyhus]

Thats always been my opinion. On target the actual neck tension (interference fit) always showed as more important than seating force (friction) in my tests and others. I do remember a friend that had a rifle with a very long throat and the bullet was seated way out. It was also a slower powder as well. That bullet did slide out. We know that because the necks didnt expand. Pressure equalized on the outside of the necks.

If people test things, stuff gets a lot clearer. You can take half a dozen cases and starting with as close to zero clearance as you can over the heel of a seated bullet....turn each subsequent case neck for .0005 more clearance.

Start with the 'zero' clearance case neck and follow the progression of the powder residue down the case necks as subsequent cases with more neck clearance are fired. The residue wave dips are also worth paying attention to.

Good shootin' -Al

 

[CA_Shooter]

Super slow motion video now shows some powder exiting the muzzle before the bullet.

This implies that the bullet is not sealing the barrel first, because the powder had to beat the bullet into the barrel to leave first