I saw a very interesting post the other day on another site regarding how a bullet exits the case in a high psi round ( > 30000 psi) and I was wondering if someone knowledgeable could weigh in. Take for example a 50000 psi round in a .308 with say 2 thousandths neck tension. Whenever the primer/powder charge goes off, is the bullet pushed out at all before the case neck releases it or are the frictional forces of the case neck (clean or with carbon/graphite) completely irrelevant because the pressure builds to a point to where the neck expands and the bullet releases? I'm asking because I think this difference would definitely play a role in how I reload in terms of trying to keep neck tension consistent.
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Advanced Marksmanship Internal Ballistics Question
- Thread starter siracusap
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Re: Internal Ballistics Question
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Savage10FCPK</div><div class="ubbcode-body"> are the frictional forces of the case neck (clean or with carbon/graphite) completely irrelevant because the pressure builds to a point to where the neck expands and the bullet releases? I'm asking because I think this difference would definitely play a role in how I reload in terms of trying to keep neck tension consistent. </div></div>
i have no idea , this is all over my head but
i doubt you can say "clean or with carbon/graphite" are completely irrelevant factors. To some extent they must be a factor. How significant is the real question... and i would have to believe it's at least noteworthy if not actually relevant to internal performance, since enough people do something about it ( IE cleaning cases , mica powder)
i cant say consistent case neck tension is as important as the tension itself. If your using low tension , then that will increase your chances of delayed ignitions, which will hurt your groups. So, it wouldn't matter if your low tension was conistent or not... since the delays you'd be getting would themselves not be consistent. ( the nature of a delay)
but , i do believe consistent neck tension is important , thats why people use bushing dies , or anneal their brass, or use runout devices.
im sorry i couldnt answer your question
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Savage10FCPK</div><div class="ubbcode-body"> are the frictional forces of the case neck (clean or with carbon/graphite) completely irrelevant because the pressure builds to a point to where the neck expands and the bullet releases? I'm asking because I think this difference would definitely play a role in how I reload in terms of trying to keep neck tension consistent. </div></div>
i have no idea , this is all over my head but
i doubt you can say "clean or with carbon/graphite" are completely irrelevant factors. To some extent they must be a factor. How significant is the real question... and i would have to believe it's at least noteworthy if not actually relevant to internal performance, since enough people do something about it ( IE cleaning cases , mica powder)
i cant say consistent case neck tension is as important as the tension itself. If your using low tension , then that will increase your chances of delayed ignitions, which will hurt your groups. So, it wouldn't matter if your low tension was conistent or not... since the delays you'd be getting would themselves not be consistent. ( the nature of a delay)
but , i do believe consistent neck tension is important , thats why people use bushing dies , or anneal their brass, or use runout devices.
im sorry i couldnt answer your question
Re: Internal Ballistics Question
I would have to say that the "neck tension" matters. The reason why neck expands is because the mouth is blocked by the bullet which is statically held by the brass, and then dynamically resisted/held by friction as the gas begins to push against the bullet base--the force of this gas has to go some where so the bullet begins to exit and the brass expands. Less frictional force would relieve pressure quicker via the bullet exiting and the brass would probably not expand as rapidly. At least that is how I'm thinking it should happen.
I would have to say that the "neck tension" matters. The reason why neck expands is because the mouth is blocked by the bullet which is statically held by the brass, and then dynamically resisted/held by friction as the gas begins to push against the bullet base--the force of this gas has to go some where so the bullet begins to exit and the brass expands. Less frictional force would relieve pressure quicker via the bullet exiting and the brass would probably not expand as rapidly. At least that is how I'm thinking it should happen.
Re: Internal Ballistics Question
My understanding is the primer actually knocks the bullet out of the case until it hits the lands (unless it's jammed of course) Then it starts to move through the barrel as the powder burns and expands. I did not believe this until I tried an experiment: for giggles I seated a primer in a 308 case, walnut media (to simulate powder) and seated a bullet with .002 neck tension. loaded into an old rifle (bullet had about .02 jump) and let it rip. Pulled back the bold and sure enough bullet was suck (surprisingly firmly) in the rifling. Had to use a cleaning rod to pop it out. Due to this, neck tension (more specificly, consistency in neck tension) is extremely important.
My understanding is the primer actually knocks the bullet out of the case until it hits the lands (unless it's jammed of course) Then it starts to move through the barrel as the powder burns and expands. I did not believe this until I tried an experiment: for giggles I seated a primer in a 308 case, walnut media (to simulate powder) and seated a bullet with .002 neck tension. loaded into an old rifle (bullet had about .02 jump) and let it rip. Pulled back the bold and sure enough bullet was suck (surprisingly firmly) in the rifling. Had to use a cleaning rod to pop it out. Due to this, neck tension (more specificly, consistency in neck tension) is extremely important.
Re: Internal Ballistics Question
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">My understanding is the primer actually knocks the bullet out of the case until it hits the lands</div></div>
I don't think that's the way its suppose to be. The crimp, eigher a crimp of neck tention is suppose to hold the bullet allowing the powder to get started burning for more constant ingnition.
To see what I mean, take a 357 case and load it with WW 296 powder. Load some bullets with out a crimp, and load some with a heavy crimp. See when one is more accurate and consistant.
Often without a crimp (or tight neck tension) you often end up with some of the powder pushed into the barrel with out burning.
Then again its different with black powder. Many of the long range BP shooters seat the bullet by hand just before loading in the chamber.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">My understanding is the primer actually knocks the bullet out of the case until it hits the lands</div></div>
I don't think that's the way its suppose to be. The crimp, eigher a crimp of neck tention is suppose to hold the bullet allowing the powder to get started burning for more constant ingnition.
To see what I mean, take a 357 case and load it with WW 296 powder. Load some bullets with out a crimp, and load some with a heavy crimp. See when one is more accurate and consistant.
Often without a crimp (or tight neck tension) you often end up with some of the powder pushed into the barrel with out burning.
Then again its different with black powder. Many of the long range BP shooters seat the bullet by hand just before loading in the chamber.
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