Staring a new series on testing with the AMP Press. What should we test?
AMP Press Testing Series
- Thread starter Sniper King 2020
- Start date
Good idea.
We normally only think of seating pressure, not what the bullet goes through coming out.
Curves with different lubes?
How about a curve for the cheapo Lee Collet Die?
We normally only think of seating pressure, not what the bullet goes through coming out.
Curves with different lubes?
How about a curve for the cheapo Lee Collet Die?
Is the bullet pushed out of the brass before the neck expands or does the neck expand before the bullet is pushed out? Does the neck expand cylindrically or does it expand conically?
Ask and yee shall receive: https://www.mecmesin.com/publications/bullet-extraction-and-seating-force-testing
lets think about this for a sec. How would it expand with a bullet in it if there is no surface area for the pressure to exert force against? pressure pushes on all surfaces exposed to powder which means the back of the bullet and inside of the case walls including back into the flash hole.
One could invert a shell on a case guage and press a rod through the flash hole to push the bullet out and measure force. could probably do that on any arbor press with a force pack or even the AMP press.
Referring to the link, why would ammo manufacturers do it?
Does it matter to them and not us?
Would like to see a force curve for the LCD in a couple different calibers.
The Collet die gets a lot of bad press when people use it wrong.
The Amp press would be perfect.
Does it matter to them and not us?
Would like to see a force curve for the LCD in a couple different calibers.
The Collet die gets a lot of bad press when people use it wrong.
The Amp press would be perfect.
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I once fused a case neck to the decapping rod inside my LCND by applying too much pressure. I can now set my AMP annealer based on how the case neck drags on the recapping rod. The LCND is pretty neat.
Based on my limited knowledge and experience with physics . . .
Pressure within the case as it ignites is uniform on all interior surfaces (think . . . how a tire expands as you pump air into it from a tiny inlet). As the pressure builds in a case, the amount of pressure to move the projectile forward through the neck is less than it takes to expand the case. As the projectile moves forward the pressure is building up rapidly and before the projectile leaves the neck, there's enough pressure to start expanding the case and the neck where the area in the neck in back of the projectile begins to expand and seal off the chamber. But, before the projectile has fully cleared the neck, the neck has expanded enough to released the projectile and as the neck is sealing the chamber some gases leak into the area between the case neck and the neck area of the chamber until the pressure fully seals off the chamber. The projectile has been released and is accelerating as the pressure continues to rise.
How hard (amount of pressure) the neck is gripping the projectile will effect the timing of the neck's release as does the amount of friction it takes to move the projectile forward. The more slippery something is, the more force it takes to keep it from moving when an adjacent force is applied. Evidence of the timing for the neck to seal the chamber can be seen on a fired case necks where powder residue has been deposited. When a charge is too light, the sealing of the chamber doesn't happen fast enough, where the powder residue escapes past the projectile around past the neck leaving deposits as far down onto the case shoulder and sometimes further.
Looking very closely at some graphs and with a little interpolation, one can kind of see that the projectile is still within the case neck area as the pressure builds enough to seal the chamber, though the projectile is in the process of moving:
Well . . . I hope this give you a better idea of the process that you're asking about.
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interesting, why is the chamber pressure different between the two?Based on my limited knowledge and experience with physics . . .
Pressure within the case as it ignites is uniform on all interior surfaces (think . . . how a tire expands as you pump air into it from a tiny inlet). As the pressure builds in a case, the amount of pressure to move the projectile forwards through the neck is less than it takes to expand the case. As the projectile moves forward the pressure is building up rapidly and before the projectile leaves the neck, there's enough pressure to start expanding the case and the neck where the area in the neck in back of the projectile begins to expand and seal off the chamber. But, before the projectile as fully cleared the neck, the neck has expanded enough to released the projectile and as the neck is sealing the chamber some gases leak into the area between the case neck and the neck area of the chamber until the pressure fully seals off the chamber. The projectile has been released and is accelerating as the pressure continues to rise.
How hard (amount of pressure) the neck is gripping the projectile will effect the timing of the necks release as does the amount of friction it takes to move the projectile forwards. The slippery something is, the more force it takes to keep it from moving when an adjacent force is applies. Evidence of the timing for the neck to seal the chamber can be seen on a fired case neck where powder residue has been deposited. When a charge is too light, the sealing of the chamber doesn't happen fast enough, where the powder residue escapes past the projectile around past the neck leaving deposits as far as the case shoulder and sometimes further.
Looking very closely at some graphs and with a little interpolation, one can kind of see that the projectile is still within the case neck area as the pressure builds enough to seal the chamber, though the projectile is in the process of moving:
View attachment 8006339 View attachment 8006340
Well . . . I hope this give you a better idea of the process that you're asking about.
It's not different, just the curve looks different because one is shown over a time period (milliseconds) and the other over distance (inches).
