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

[Ringostar]

Here’s another possible variable. What about neck thickness?

 

[243winxb]

Cartridge brass- C26000 material starts to yield at 15,000 PSI when soft, annealed.

Primers produce around 23,000 PSI on firing, in the pocket. . No powder.

In 243 Win., a starting load of IMR 4350 with a 68/70 gr bullet will not expand fired necks. NO annealing .
A near maximum loading will expand necks.

Comes down to PSI and powder burn rate.

https://discover.dtic.mil/

Primer Output and Initial Projectile Motion for
5.56- and 7.62-mm Ammunition

These studies have shown that the primer output alone can greatly influence the initial motion of a small-caliber projectile. The primer is capable of producing enough force to debullet the projectile and begin the engraving process prior to any significant propellant burning.

 

[243winxb]

Bullet hold & crimp . The 5.56 round has a minimum bullet pull of 35 pounds.
A crimp raises start pressure & helps powder burn.

 

[davidjoe]

On the theory that the barrel is only containing pressure behind the bullet, not in front of it, the bullet must make way for direct lateral pressure to contact the neck and therefore expand it.

With high enough pressure from a crimp combined with the engraving, it is acting upon the neck like your “foot” pushed through a sock. A thin neck, or a loose fitting sock easily expands and it’s only fair to the question to disregard the fact that if we pull on any part of a set table cloth, there is a tiny and different amount of force applied at each place of it.

 

[davidjoe]

If you thin out your necks enough, you can see that a the bullet bulges it out exactly at the contact spot, which is telling.

… But with very weak containment of pressure, the bullet escapes the neck, pressure peaks in a few inches and expands the whole cartridge. My best guess.

I do believe it is generally true that it is much harder to force a bullet into the barrel than expand a neck, probably by 10X, so as the bullet clears each part of the neck, I could envision it beginning to expand, with the thicker portions probably snapping under peak.

 

[dgeesaman]

Interesting concept!

I would ask 2 additional questions. How much pressure would it take to get bullet into the bore and completely out of case. Is that enough pressure to open neck?

It’s a simple system with wildly complicated friction factors. So the calculations are clear (might need an explicit FEA to solve the simultaneous neck expansion and bullet pressure) but the amount of friction could be different between, say, seating and firing.

That said, as a rough answer, it’s less than the force required to seat the uncrimped bullet.

So let’s say it took 50lb to seat the bullet, then using a 6mm bullet the equivalent pressure is 1000psi.

 

[JEFFPPC]

I have read numerous articles from industry sources over the last many years about this. They have always stated the neck expands first. So until I see contrary validated information I will go with that. I do know this. It is what it is and any conjecture shooters formulate in their heads will neither matter or probably be correct.

 

[CA_Shooter]

I have read numerous articles from industry sources over the last many years about this. They have always stated the neck expands first. So until I see contrary validated information I will go with that. I do know this. It is what it is and any conjecture shooters formulate in their heads will neither matter or probably be correct.

I don't know the science to really have an opinion which is true.

However, I can say that if the neck expands first then that means donuts don't make a difference

 

[dgeesaman]

I have read numerous articles from industry sources over the last many years about this. They have always stated the neck expands first. So until I see contrary validated information I will go with that. I do know this. It is what it is and any conjecture shooters formulate in their heads will neither matter or probably be correct.

Industry experts say tuners don't work

 

[davidjoe]

I have read numerous articles from industry sources over the last many years about this. They have always stated the neck expands first. So until I see contrary validated information I will go with that. I do know this. It is what it is and any conjecture shooters formulate in their heads will neither matter or probably be correct.

It is hard to explain blow by if the neck doesn’t first open, allowing it. I don’t think a squib round permits any blow by, so it had to have occurred very early. But as others point out, if it opens, then bullet drag inside the neck isn’t a major “thing.”

 

[rwj]

I have read numerous articles from industry sources over the last many years about this. They have always stated the neck expands first. So until I see contrary validated information I will go with that. I do know this. It is what it is and any conjecture shooters formulate in their heads will neither matter or probably be correct.

Please provide citations as they hopefully contain data…

 

[DShortt]

I have no idea. I do not have access to equipment to attempt to measure this even if I had a theory I wanted to prove.
At the end of the day, it's a 'chicken or the egg' type of question. The chicken exists. The bullet left the barrel.

 

[William Vogel]

Thinking it starts with a pressure wave from the primer, then the expanding gases, which will push on the shoulder and open the base of the neck, which then travels as a wave alongside the bullet, opening the neck, and it's the the small escape of gas in the process of opening of the neck, that dirties the exterior of the neck. If the bullet was blocking gases at that point, you get collapsed shoulders. Primers can move bullets, but, I'm not convinced it's fast enough on heavier bullets, to move the bullet much. I don't know how much pressure it takes to move the shoulder and open the case neck, but, the neck carbon would indicate to me it's pretty close to what it takes to start to move the bullet, apparently a hair less, but enough to seal the neck/shoulder juncture first. Thinking brass thickness on neck and shoulder will have some bearing on that timing also. If the rebounding wave theory is right, the first wave from primer ignition has to seal the shoulder, the second one that pushes the base back to the bolt face and stretches the case, has to be the one that does the bulk of the work on the bullet on the return trip to the neck. Sure there is likely a whole bunch more than that involved that I don't know squat about, and some points I probably missed or got wrong. But, that's how my old addlepated beanbox interprets it.

I think exactly the way you do about it. Because the pressure ramps up so fast, I believe it expands from the back of the cartridge forward and because the brass gets thinner as it progresses towards the neck it has the ability to stretch the brass along the web forcing the case head back to the bolt face. This being the reason we only bump the shoulder back just enough to chamber properly and minimize the brass stretch.

 

[Albany Mountain]

Interesting concept!

I would ask 2 additional questions. How much pressure would it take to get bullet into the bore and completely out of case. Is that enough pressure to open neck?

It takes the same amount of pressure it took when the bullet was installed into the case. Probably not much while the increasing pressure as bullet goes down the bore, would expand all exposed internal brass, including the neck.

 

[JEFFPPC]

Industry experts say tuners don't work

Hornady is the only one I know, but I can prove for my own satisfaction they are wrong. Thus I don't view them as experts but corporate salesmen. Of course you can if you choose. Do you have an opinion or just looking to argue? If the latter I don't have time for you.

 

[JEFFPPC]

I don't know the science to really have an opinion which is true.

However, I can say that if the neck expands first then that means donuts don't matter. Who said they do, wasn't me. I have never had a donut problem. In a lot of this there may be no accepted science just many folks ideas about things I don't waste time on. My concern is what my target says and am I tuned into my flags.

 

[dgeesaman]

Hornady is the only one I know, but I can prove for my own satisfaction they are wrong. Thus I don't view them as experts but corporate salesmen. Of course you can if you choose. Do you have an opinion or just looking to argue? If the latter I don't have time for you.

I don't think the vast majority of 'industry' people who are talking to the public have much useful to say. They're selling things and/or oversimplifying the actual reality and mostly their information aligns with the story that helps them make business.

 

[Fast14riot]

Having seen the video, it shows how we can fire form brass, moving the shoulder 1/8" in some cases before the bullet leaves the barrel. The first constriction the expanding gasses encounter is the tapered shoulder (smaller volume than case body). A bullet has a lot more grip with an interference fit in brass than say something like snow in the barrel, which is why it'll blow up radially before pushing it out.

 

[Sniperhandle]

Cartridge brass- C26000 material starts to yield at 15,000 PSI when soft, annealed.

Primers produce around 23,000 PSI on firing, in the pocket. . No powder.

In 243 Win., a starting load of IMR 4350 with a 68/70 gr bullet will not expand fired necks. NO annealing .
A near maximum loading will expand necks.

Comes down to PSI and powder burn rate.

https://discover.dtic.mil/

Primer Output and Initial Projectile Motion for
5.56- and 7.62-mm Ammunition

These studies have shown that the primer output alone can greatly influence the initial motion of a small-caliber projectile. The primer is capable of producing enough force to debullet the projectile and begin the engraving process prior to any significant propellant burning.

I used to shoot primer powered only Speer Plastic bullets in my old shop for fun out of my 1911's. One time I grabbed the Magnum Rifle primers on accident, It went completely though my little target trap and then made a perfectly round hole through my old wooden shop door, Probably around 3/8 thick, Of course the report was much louder too. I couldn't believe it.

 

[DaveTooley]

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.