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

[gunsandgunsmithing]

Interesting thread and I've followed along..somewhat.

Gonna just toss out an analogy and see what others think, is all
Lets imagine the neck were ultra light and pliable, like a soft and very thin plastic with say, a silicone consistency vs brass. Another analogy..a feather...soft and light.

Now, if the bullet is seated below this theoretical feather light and soft neck, do will still believe it doesn't move before the far heavier bullet moves?

It's not a trick question and I'm in the crowd that thinks BOTH can happen at the same time, but does my analogy change anything regarding the physics? My thinking is that under 65,000psi, a .010 thick piece of brass case neck...is a feather. Am I wrong?

Also, I tend to think that jamming hard minimizes whatever effect neck tension has, in regard to when the bullet begins to move. If so, jumping is allowing pressure to BUILD higher before the bullet begins to engrave. Sorta a running start at the lands vs a standing start because more time is given for more powder to begin to produce gas.

Just spit balling here but curious what others say. FWIW, I have virtually always found a great load with some amount of jam. Not saying one way is better or worse, just different and one way MIGHT minimize the variables of neck tension and thickness better more than the other.

 

[Wild Bill IV]

Interesting thread and I've followed along..somewhat.

Gonna just toss out an analogy and see what others think, is all
Lets imagine the neck were ultra light and pliable, like a soft and very thin plastic with say, a silicone consistency vs brass. Another analogy..a feather...soft and light.

Now, if the bullet is seated below this theoretical feather light and soft neck, do will still believe it doesn't move before the far heavier bullet moves?

It's not a trick question and I'm in the crowd that thinks BOTH can happen at the same time, but does my analogy change anything regarding the physics? My thinking is that under 65,000psi, a .010 thick piece of brass case neck...is a feather. Am I wrong?

Also, I tend to think that jamming hard minimizes whatever effect neck tension has, in regard to when the bullet begins to move. If so, jumping is allowing pressure to BUILD higher before the bullet begins to engrave. Sorta a running start at the lands vs a standing start because more time is given for more powder to begin to produce gas.

Just spit balling here but curious what others say. FWIW, I have virtually always found a great load with some amount of jam. Not saying one way is better or worse, just different and one way MIGHT minimize the variables of neck tension and thickness better more than the other.

After studies in calculus and analytical geometry, you study minimums, maximums, peaks, and inflection points of grafts and the functions of those grafts for determining where problems probably occur and how efficient the curve is!!!! 1st and 2nd derivatives of the curve formula are evaluated for mins, max, and inflection points!!! The peak is where the slope of the formula is zero!!!

A jumping bullet will create a slight drop in pressure accelerstion and then a fast built up of pressure before driving the bullet fully into the rifling!! This creates a slight downward wave in the pressure curve causing an inflection point (A point of change to examine for inefficiency)!! The bullet (looking at nanoseconds of time) will undergo and acceleration (the jump), a slight deceleration (jammed into the rifling and waiting for the pressure to build enough to force the bullet fully into the rifling), and back to an acceleration (running the rifling)!! Not a continuous acceleration rate for efficiency and repeatability!!!

A jammed bullet will build pressure at the start of the full engagement of the bullet to the rifling more smoothly in the pressure curve and will have no wave in the smooth and continuous curve creating a continuous acceleration rate of the bullet!!! This allows for better repeatability and efficiency!!!

 

[DShortt]

Suppose it were proven definitively one way or another.

What would you do differently?

 

[dellet]

Suppose it were proven definitively one way or another.

What would you do differently?

On low pressure loads I would flare the case mouth slightly to help seal the chamber and keep gasses from blowing back and collapse the case.

 

[Wild Bill IV]

Time to do the math and end this thread!!

Force = pressure x area!!!

For this example, I will use a 264 caliber bullet where the neck will expand 0.005" more than the bullet diameter using 65,000 psi max pressure!!! The area of the bullet base is 0.0547 sq inches!!! The area of the full expanded neck will be 0.0570 sq inches!! The potential area between the bullet and full expanded neck is 0.0023 sq inches!!!

Looking at the forces between the bullet base and the area between the bullet/expanded neck yields:
3,555.5 lbs of force on the bullet base!! Yeah, over 1-3/4 TONS!!!!
149.5 lbs of force between the bullet/neck!!! ONLY 4% OF THE BULLET FORCE!!!
Or, the bullet feel 25 time more force than the potential gap force!!

For a minimal neck 0.002" clearance, the gap force would be 0.0009 sq in x 65000 psi = 58.5 lbs or 1.6% of the bullet force!!! Or the bullet feels over 60 time more force!!!

THE BULLET MOVES FIRST!! AND IS INTO THE RIFLING LONG BEFORE (IN NANOSECONDS) THE NECK EXPANDS!!!! Hence, powder residue on the outside of the neck!!!!

 

[ELR LVR]

Time to do the math and end this thread!!

Force = pressure x area!!!

For this example, I will use a 264 caliber bullet where the neck will expand 0.005" more than the bullet diameter using 65,000 psi max pressure!!! The area of the bullet base is 0.0547 sq inches!!! The area of the full expanded neck will be 0.0570 sq inches!! The potential area between the bullet and full expanded neck is 0.0023 sq inches!!!

Looking at the forces between the bullet base and the area between the bullet/expanded neck yields:
3,555.5 lbs of force on the bullet base!!
149.5 lbs of force between the bullet/neck!!! ONLY 4% OF THE BULLET FORCE!!!
Or, the bullet feel 25 time more force than the potential gap force!!

For a minimal neck 0.002" clearance, the gap force would be 0.0009 sq in x 65000 psi = 58.5 lbs or 1.6% of the bullet force!!! Or the bullet feeld 60 time more force!!!

THE BULLET MOVES FIRST!! AND IS INTO THE RIFLING LONG BEFORE (IN NANOSECONDS) THE NECK EXPANDS!!!! Hence, powder residue on the outside of the neck!!!!

Thanks for doing the math for us Wild Bill
Do you believe that---
As opposed to the neck---staying the same dia. until the bullet finally leaves, then suddenly expanding all at once....
----That instead the neck rolls outward behind the bullet AS, the bullet is exiting, and any forces behind the bullet base --- expand and roll the case neck outward?

 

[Wild Bill IV]

Thanks for doing the math for us Wild Bill
Do you believe that---
As opposed to the neck---staying the same dia. until the bullet finally leaves, then suddenly expanding all at once....
----That instead the neck rolls outward behind the bullet AS, the bullet is exiting, and any forces behind the bullet base --- expand and roll the case neck outward?

If the neck rolls out behind the bullet, there would be no residue on the outside of the neck!!!! The neck expands near the peak of the pressure curve where the high pressure gases are flowing and the unburnt powder, but still burning tightly pact column following the bullet!! Where the accelerating bullets is increasing the volume behind the bullet turn the pressure curve flatter or more downward, but still not at peak!!!! The pressure at this point is being generated in the barrel, causing back pressure and opening the case neck!!!
ANALOGY: Think about the bulge in a garden hose about ready to rupture with the sprinkle going!! Shut the pressure off at the sprinkler, the puppy pops!!!

 

[Webster]

Time to do the math and end this thread!!

Force = pressure x area!!!

For this example, I will use a 264 caliber bullet where the neck will expand 0.005" more than the bullet diameter using 65,000 psi max pressure!!! The area of the bullet base is 0.0547 sq inches!!! The area of the full expanded neck will be 0.0570 sq inches!! The potential area between the bullet and full expanded neck is 0.0023 sq inches!!!

Looking at the forces between the bullet base and the area between the bullet/expanded neck yields:
3,555.5 lbs of force on the bullet base!!
149.5 lbs of force between the bullet/neck!!! ONLY 4% OF THE BULLET FORCE!!!
Or, the bullet feel 25 time more force than the potential gap force!!

For a minimal neck 0.002" clearance, the gap force would be 0.0009 sq in x 65000 psi = 58.5 lbs or 1.6% of the bullet force!!! Or the bullet feeld 60 time more force!!!

THE BULLET MOVES FIRST!! AND IS INTO THE RIFLING LONG BEFORE (IN NANOSECONDS) THE NECK EXPANDS!!!! Hence, powder residue on the outside of the neck!!!!

I usually reply to the last reply so I don't have to go nuts looking at a bunch of replies. My guess is that none of us will ever have the equipment to determine what’s going on. We can only guess. It would probably take a $100,000 research program by the Defense Dept. Nothing wrong with the old simple theory, do what shoots small on the target. Most of us will never shoot at the level to see tiny improvements. Even if you understood what was going on you probably couldn’t do anything with the information.

Side issue. whats going on when you see a different carbon pattern on the case neck with a 2 compared to a 3 lug bolt?

 

[ELR LVR]

I usually reply to the last reply so I don't have to go nuts looking at a bunch of replies. My guess is that none of us will ever have the equipment to determine what’s going on. We can only guess. It would probably take a $100,000 research program by the Defense Dept. Nothing wrong with the old simple theory, do what shoots small on the target. Most of us will never shoot at the level to see tiny improvements. Even if you understood what was going on you probably couldn’t do anything with the information.

Side issue. whats going on when you see a different carbon pattern on the case neck with a 2 compared to a 3 lug bolt?

What I am unfortunately leading up to with Some of these
"tiny improvemts"
---Is it perhaps some of them are more of a placebo effect
if we feel more confident we have applied more neck tension for instance
then we may be more confident in shooting that load .050" smaller lol
-------------
Unless the utmost consitency is there to prove it, which would take a rail gun
I lean more toward we feel better so shoot better
with some of our theories in experimentation.
IE:
"I feel, if I make full contact with my barrel tenon threads to the action for example, my guns are more accurate" That is my plcebo effect but with decent theory to back it.
We are more confident to shoot better and enter with a better mindset if we use
Lapua brass vs Remington brass
Berger vs Noslers
Krieger vs Bartlein
Tight neck tension vs less
Etc
------------
FWIW I use as little neck tension as possible to just hold the bullet
And get good consistent results
But I try to stress that making decisions based solely on feelings, leads usually to nothing more than placebo effects, without good "Consistency" in the evidence to back a claim.
----Something to back the Placebo effect theory/ in the opposite manner
Has anyone ever somehow,? shot badly on any given day with an accurate gun and a good load?
------------
What I find difficult to discern when this happens is knowing if my gun is actually slightly out of tune
or if Im just "Not in the Zone " yet

 

[Wild Bill IV]

I usually reply to the last reply so I don't have to go nuts looking at a bunch of replies. My guess is that none of us will ever have the equipment to determine what’s going on. We can only guess. It would probably take a $100,000 research program by the Defense Dept. Nothing wrong with the old simple theory, do what shoots small on the target. Most of us will never shoot at the level to see tiny improvements. Even if you understood what was going on you probably couldn’t do anything with the information.

Side issue. whats going on when you see a different carbon pattern on the case neck with a 2 compared to a 3 lug bolt?

This is where I get most of my information!!! I've been looking at Military testing grounds and ballistics labs reports since the start of the internet where the data streamed through the land lines (Analog to digital with a PC computer MODEM card)!!! Most of those reports were from the 40s to early 70s before all testing was combined to the single location at Aberdeen, Virginia!!! I read the reports and studied the derivations of the mathematical equations and the physics principles involved!!!

 

[Wild Bill IV]

I usually reply to the last reply so I don't have to go nuts looking at a bunch of replies. My guess is that none of us will ever have the equipment to determine what’s going on. We can only guess. It would probably take a $100,000 research program by the Defense Dept. Nothing wrong with the old simple theory, do what shoots small on the target. Most of us will never shoot at the level to see tiny improvements. Even if you understood what was going on you probably couldn’t do anything with the information.

Side issue. whats going on when you see a different carbon pattern on the case neck with a 2 compared to a 3 lug bolt?

2lug vs 3lug!! Simply stated, DEGREES OF FREEDOM!! 2lug has 180° DOF!! 3lug has 120°DOF!! The 2lug can rock either way at 90° to the centerline of the 2lugs!!! 2lugs are like a 2 leg chair!! 3lugs are like a 3 leg chair!!! Which is more stable to sit in????

 

[Wild Bill IV]

BASIC 101 INTERNAL BALLISTICS INVOLVING BASIC CONCEPTS ON THE CASE NECK:
It's time to expand further and determine when the case neck expands from my reply above with TIME TO DO THE MATH followed by FORCE = PRESSURE x AREA!! The pressure and forces are almost astronomical!!!

CONCEPTS USED TO DETERMINE WHEN THE NECK EXPANDS:
An understanding of flow velocity (a vector) and pressure vectors is required!! When there is flow, the outward pressure vector component is way lower in magnitude (psi) than the directed pressure vector component in the flow velocity direction!! A pressure differential creates flow and the cross sectional area determines how fast the flow moves (the magnitude - SPEED of the flow velocity vector)!

A SIMPLE ANALOGY OF DESCRIBING THESE CONCEPTS:
String out a 50 foot heavy rubber coated air hose, attached to a 150-200psi regulated compressor at one end, and a blow nozzle with the "STUPID AND WORTHLESS" OHSA approve safety orfice removed or heavily modified at the other end!! Maximizing flow is required for this visualization!!! Keep some of the memory coil in hose!!! When there is no flow, the full pressure is directed outward and the hose is slightly shortened due to the outward stretch of the hose!!! Triggering the blow nozzle creates directed flow of the compressed air and the outward pressure is relaxed causing the hose to "JUMP" due to inward recoil of the elastic hose walls and the hose becomes longer!!! Releasing the trigger stops the flow of the compressed air caused a pressure wave directed back to the tank!! The hose "BOUNCES" because the flow stops and the pressure is redirected outward on the hose walls causing it to swell and shorting the hoses length!! This recoil effect, BOUNCING, of the hose walls is noticeable in high pressure framing nail guns and roof staplers where the flow suddenly starts/stops from the compressed air flow source to these pneumatics devices!!! The sudden stop in flow is also called HAMMERING in the plumbing profession!!!!

APPLYING THESE CONCEPTS USING THE ANALOGY:
The same thing happens inside the fired firearm!!! With the bullet moving down the barrel with the tightly packed unburnt, but still burning powder column, the volume increases causing a PRESSURE DIFFERENTIAL which creates the flow of hot gases coming out of the case and the neck sees very little outward pressure, just like the triggered blow nozzle reduces the outward pressure on the hose!! The turbulent flow of hot gases, caused by the pressure differential of the case and barrel thru the neck, deposits powder residue on the outside of the neck!!

At a certain critical point, the pressure in the case is equal to the pressure being generated from the column of powder behind the bullet, which is in the barrel, and stops the flow of gases coming out of the case (PRESSURE DIFF IS ZERO OR NONEXISTENT)! Now, the pressure component is directed outward and THE NECK EXPANDS, or HAMMERED out in the plumbing field, just like the reverse pressure shock wave generated by a quick release of the blow nozzle trigger swells the hose causing the hose to jump!!

CONCLUSION:
Where does the peak pressure come from??? The final burnt powder is in the barrel, not in the case!!! There is actually a little reverse flow back into the case!!! THE PEAK PRESSURE IS GENERATED IN THE BARREL, AND NOT IN THE CASE!!!!

AS AN INDUSTRIAL PHYSIST (MORE APPLIED SCIENCE THAN THEORETICAL), I KNOW A LITTLE OF EVERYTHING, AND A LOT OF NOTHING!!!!!!!

ELON MUSK: Physics is based on Principles, not Analogy!
Wild Bill's Philosophical Responded to Elon Musk: On the contrary, Mr. Musk, the Laymen Scientist needs a Representative Analogy to Visualise Each Principle of Physics!!!

 

[jackieschmidt]

Does the object of this discussion involve Long Range, (600+ yards), or Short Range, (300 yards and less).

In most of my 6PPC or 30BR loads, I use such a light neck tension that whether the neck expands before, during, or after the bullet moves seems virtually a non issue.

 

[Alex Wheeler]

Jackie there was no oject other than to start a discussion.

 

[jackieschmidt]

Jackie there was no oject other than to start a discussion.

Ok.

 

[WSnyder]

Suppose it were proven definitively one way or another.

What would you do differently?

That^^^ It just does what it does. Reminds me of that movie

 

[old_heli_logger]

Very interesting discussion, thanks for posting this @Alex Wheeler
I don't understand all I know about this.

My EE answer always starts with, "it depends"...

My understanding has always been that the primer is an explosion and the powder column is a flammable coated with deterrent. It takes a bit to ignite the powder column, so the primer explosion pushes all the powder forward and pushes the bullet into the rifling before very much of the powder actually starts to burn. Please correct me if I'm wrong.

Where's McGuffey when we need him? I think that was his name

 

[Straightshooter1]

Time to do the math and end this thread!!

Force = pressure x area!!!

For this example, I will use a 264 caliber bullet where the neck will expand 0.005" more than the bullet diameter using 65,000 psi max pressure!!! The area of the bullet base is 0.0547 sq inches!!! The area of the full expanded neck will be 0.0570 sq inches!! The potential area between the bullet and full expanded neck is 0.0023 sq inches!!!

Looking at the forces between the bullet base and the area between the bullet/expanded neck yields:
3,555.5 lbs of force on the bullet base!! Yeah, over 1-3/4 TONS!!!!
149.5 lbs of force between the bullet/neck!!! ONLY 4% OF THE BULLET FORCE!!!
Or, the bullet feel 25 time more force than the potential gap force!!

For a minimal neck 0.002" clearance, the gap force would be 0.0009 sq in x 65000 psi = 58.5 lbs or 1.6% of the bullet force!!! Or the bullet feels over 60 time more force!!!

THE BULLET MOVES FIRST!! AND IS INTO THE RIFLING LONG BEFORE (IN NANOSECONDS) THE NECK EXPANDS!!!! Hence, powder residue on the outside of the neck!!!!

What about inertia?

Seems like there'd be an issue for the speed of the expanding gases acting the mass of the bullet that might require more force than simple math shows???

 

[X Count]

Look at it this way. . .

If the neck does not expand before the bullet leaves the case, then why do we need "sufficient neck clearance" to achieve very good accuracy?

If the bullet left the case before the neck expanded we could get away with minimal to zero neck clearance, providing the case could freely chamber.

 

[Wild Bill IV]

What about inertia?

Seems like there'd be an issue for the speed of the expanding gases acting the mass of the bullet that might require more force than simple math shows???

Doesn't matter what the acceleration of the pressure is!!! The areas, and the ratios don't change!!! The bullet will always see 25 times more force on the base of the bullet than the gap (primary example) and 60 times more force in the 2nd! Doesn't matter if it is a 100 grain bullet or a 200 grain bullet, as long as the caliber stays the same, ie 264 caliber for my example. It doesn't matter if it is a boat tail or flat base, they still have the same exposed area to the pressure!! I was simple stating how much max force (Push) was imposed on the base of the 264 caliber bullets base at peak pressure (65K psi)!!

The formula is a linear, meaning it has a straight line with the slope angle being the base area and the intersection will be at 0,0!!! The graft will have the force on the y-axis, and pressure on the x- axis. Therefore, the force will directly change proportionally to the change in pressure by the factor of the fixed area!!!

An understanding of the scientific terms is needed!!
65,000 psi (Pressure or pushing) is equivalent to a Weight of 32.5 tons distributed on a 1" x 1" surface!! Weight is a force! Now, if a change in area occurs, the weight distribution will also change, changing calculated force acting on that a changed area!!! PRESSURE IS A PUSHING FORCE DIVIDED BY AN AMERICAN STANDARD UNIT AREA!!!

INERTIA falls out of the equation because we are using NEWTON'S 2rd LAW!! Newton's law of force acting on a body! Force = pressure x area!!! The Force or push (lb) on an area exposed to the pressure = A measured force or push (lbs)/standard unit area (1 sq in) times a measured and/or calculated surface area (sq in) exposed to that pressure!!!

However, Newton's 3rd Law (Action/Reaction forces) is being used, and abused by most forum members that don't understand this PROVEN LAW of NATURE!! The Term TENSION does not exist unless there is an equal, but opposite force acting against Tension!! When talking about forces, and I stress plurality here, involving the neck and bullet, Tension (the inward pull towards the center axis in a cylindrical coordinate system) of the neck IS EQUAL TO the COMPRESSION (the outward push from the same center axis in the same cylindrical coordinate system) of the bullet in the neck! T=C, therefore the summation is ZERO (T-C=0)!! A body does not possess force, but it possess inertia or momentum (Newton's 1st law)!!! Tension by itself violates Newton's 1st Law!!
--------------A LIMP ROPE HAS NO TENSION!!!!!!!!!!!!!!!!
--------------A CASE NECK, WITH NO BULLET IN THE NECK, HAS NO TENSION!!!!!!
--------------A BULLET, NOT SEATED, HAS NO COMPRESSION!!!!!!!

If you want to be scientific, use scientific terminology!!
The term "Tension" needs to be replace by IF (Engineering standards class interference fit)!! Interference fit can be changed with neck bushings and/or mandrels!!!! And, must interference fits use presses to mate or set the two mechanical bodies together!!