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

[Alex Wheeler]

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

Facebook

www.facebook.com

 

[G Liles]

I would think that the pressure building from the case head would push the bullet out before the neck expands. This is just an old country boy’s thinking!! I’m sure there are far more knowledgeable minds that have different opinions.

 

[wedgy]

link is not working for me

 

[Coyotefurharvester]

If the mass of the bullet requires more energy to start motion than the energy required to expand the neck, the bullet isn't moving first.

 

[rwj]

It appears the FB poster has either deleted, or restricted who can view, the material.

Though not based in data, my “SWAG” would be that internal case pressure would cause the bullet to start sliding before the neck expands to fully release if the bullet is “jumped.” If the bullet is jammed into the lands, I’d place my money on the case neck expanding to full release before the bullet moves.

Interesting question, and hopefully an equally interesting thread!

 

[G Liles]

If the mass of the bullet requires more energy to start motion than the energy required to expand the neck, the bullet isn't moving first.

If this is true then why worry about neck tension?

 

[dgeesaman]

It has to be both together simultaneously.

Pressure behind the bullet makes it want to more forward. Friction from neck tension resists. Also pressure inside the case pushes outward on the bottom end of the neck, and as pressure builds that reduces neck tension.

 

[ORjeff]

Pressure can not be applied to the inside of the neck until the bullet has moved out of the way. So, first the bullet moves forward then as the neck is exposed it expands, beginning at the rear.

 

[dgeesaman]

Pressure can not be applied to the inside of the neck until the bullet has moved out of the way. So, first the bullet moves forward then as the neck is exposed it expands, beginning at the rear.

Only when the bullet is too long for the neck

 

[William Vogel]

What happens to the air around the brass and the chamber?

 

[Coyotefurharvester]

If this is true then why worry about neck tension?

Because it changes the elasticity of the neck portion of the case(just as annealing). Smaller/tighter increases the energy required to start expansion. Just speculation on my part and basic physics.

 

[ELR LVR]

If this is true then why worry about neck tension?

This is where I'm at in my thinking now as well.
I dont think neck tension matters a whole lot.
I've seen equally great groups in neck tension ranging from ----
1. strips copper off the bullet to 2. almost seat bullets with your finger
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Also - I'd say the bullet moves first,
---otherwise how would the outside of our necks get smoked with carbon unless the bullet first got out of the way, for gasses to escape the case and creep around the neck,
then as the bullet enters enough into the rifling to slow itself down does chamber pressure then build enough to balloon the case neck to tightly seal against the chamber.
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How can gasses get around the neck, if the neck first expanded against the chamber before the bullet moves?
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Now maybe it's Both / one or the other can happen, DEPENDING UPON your neck tension
and I'm more toward that theory
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I use light neck tension and most of my case necks are lightly carbon smoked
However when I have used heavy neck tension with Lapua brass, I seem to notice little to no smoke on the necks
which leads me to believe in that instance..... that the neck holds the bullet until pressure builds enough to balloon the case and seal against the chamber while then releasing the bullet.
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Everyone try this
Chamber a round with only a primer and no powder
See if your bullet leaves the case and sticks into the rifling
If so, then we know the primer going off alone spits the bullet out

 

[JFrank]

Everyone try this
Chamber a round with only a primer and no powder
See if your bullet leaves the case and sticks into the rifling
If so, then we know the primer going off alone spits the bullet out

Been there done that.
Nothing happens beyond a click of the firing pin.

 

[209jones]

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.

 

[Bottom Fodder]

Here’s my 2cents which is worth about 1cent neck expansion as bullet moves forward the higher neck tension “ may increase pressure” but also helps hold bullet in place if you are jamming the bullet in the lands which also increase pressure and I have learned some cartage, bullet, powder combinations shoot better with higher pressure ‍
.
,

 

[Chaotik]

In my testing and experience I have never seen a correlation between neck friction (measured by the seating force of the bullet) and the velocity of the bullet. It just doesn't matter. This suggests to me that the bullet is released prior to any movement of the projectile.

 

[dgeesaman]

Been there done that.
Nothing happens beyond a click of the firing pin.

Yep it snaps forward into the lands and stays there.

 

[Vin81]

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?

 

[SMITTY33]

Yep it snaps forward into the lands and stays there.

Correct, I used this method 40 years ago to learn where max jamb was on an old .243 that I had that would not shoot with any jump, but was a laser at jamb. Years later when I got my first Lyman bore scope I learned the lead in to the chamber was rough as a cob. I actually got the idea from a near disaster shooting reloads out of S&W 19, when I didnt notice any recoil on a rapid fire string about 3 shots in. Fortunatley I Had the presence of mind to check, rotated the cylinder open to see the wadcutter sticking out the back of the barrel.
I was shooting a training round robin loading of 38 special and 357Mag that my brother and I were random loading the revolver for each other with. Very Lucky day for me that I will never forget, the next round was a 357Mag round !! I have learned a lot over the years ... and would NOT Recomend anybody ever using that system for finding Jamb !! Its amazing that any of us make it to being old with the "Great Ideas" we can come up with !!

 

[Fuj]

it's always going to be the path of least resistance. The variables
leading to that point such as neck tension, jump/jam. bullet base
profile such as flat base or boat tail, any lube used, included just
the natural carbon built up, no lube clean necks, anneal, no anneal,
pooch loads in a BR verses a 28 Nosler......yadda, yadda !!