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Rifles, Reloading, Optics, Equipment
Reloading
Neck Tension vs Bullet Seating & Release Pressure - Lessons Learned
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<blockquote data-quote="mrdinapoli" data-source="post: 2762477" data-attributes="member: 93495"><p>Mikecr and Tiny Tim, </p><p>I agree with both your comments. What we are commonly calling neck tension (NT), is technically termed hoop tension or hoop stress. It appears from my understanding that we can't, or at least can't easily, measure hoop tension. Therefore we are measuring NT as a surrogate, which will have some correlation but will have limitations and different influencing variables. Further, bullet release pressure or friction has many more controlling variables than NT alone, such as inside neck smoothness, the presence of fouling in the neck, brushing, lubricants, brass properties, brass hardness, bullet construction, jacket materials, cold welding, etc, as well as length of neck reduction as Mikecr pointed out. I also agree that the way bullets exit the case is primarily by release of the bullet as the case neck and shoulder are blown out to chamber dimensions by combustion. Otherwise, as Mikecr mentioned in another post, the rifle would likely explode due to excessive pressure buildup. However, I think we can all agree that neck tension / bullet friction plays at least some effect in early pressure buildup and bullet release. If there was no interference or friction, the bullet would likely move even micron as pressure built prior to sufficient pressure building to expand the case neck. Even slight bullet movement will change case capacity and internal combustion dynamics. This is supported by countless findings over many years and many disciplines that have shown or reported differences in velocity, accuracy, and SD with only changes in NT. The question and source of controversy is how much of a role does NT play in this process. Is it so small as to be unmeasurable and/or statistically insignificant, or does it play a larger and more measurable role? This is where further studies and a different set of equipment will be required.</p><p></p><p>I started out to answer one question regarding seating pressure differences between standard and Hammer bullets, and this morphed into curiosity about release pressures — whether truly relevant or not. However, I feel that some of the most interesting information found revolved around neck reduction, transition point of elastic to plastic deformation, maximum obtainable NT, and the role of mandrel use in obtaining maximum NT.</p><p></p><p>Most importantly, I feel that there will be a maximum amount of neck reduction, after which additional NT will not be possible, and that anything over this amount will only serve to overwork brass and potentially damage bullets. The only other effectors that come into play are the length of neck reduced (as Mikecr suggested), and whether a mandrel is used to expand the neck to desired size as the last step, which appears to serve in creating additional inwardly directed elastic neck tension. Any additional bullet friction adding to release pressure increases will likely be achieved only by the variables mentioned above (inside neck smoothness, the presence of fouling in the neck, brushing, lubricants, brass properties, brass hardness, bullet construction, jacket materials, cold welding, etc). Again, the question returns to does this matter at all, and if so, how much. I believe that in the end, this will be shown to a measurable effect on accuracy, velocity, and precision. However, I believe the effect will be small in relation to other variables such as powder, bullets, primers, and barrels. These effects will likely only be fully realizable to those with highly accurate equipment and excellent technique.</p><p></p><p>Further, I agree with Tiny Tim that there a significant number of variables contributing to the topics described above, as well as to accuracy in general — probably even more than we currently understand and can measure. To further complicate matters, all of these interacting events occur and influence each other in the course of milliseconds. I have no way of measuring pressure. However, I am curious as to how the above measurably affects accuracy, velocity, and precision, and this is something that can be done even if we can't accurately measure the pieces of the puzzle or don't fully understand the process. I plan to look into this further, but I would really like to have an AMP press so I can much more accurately and consistently measure seating and release variables to make the data more usable. It is too easy to over or under interpret data when the background noise is large. I would also like to add neck crimping to the test groups as I feel this will likely tease out additional info.</p><p></p><p>Great discussion. Thanks, Mike D</p></blockquote><p></p>
[QUOTE="mrdinapoli, post: 2762477, member: 93495"] Mikecr and Tiny Tim, I agree with both your comments. What we are commonly calling neck tension (NT), is technically termed hoop tension or hoop stress. It appears from my understanding that we can’t, or at least can’t easily, measure hoop tension. Therefore we are measuring NT as a surrogate, which will have some correlation but will have limitations and different influencing variables. Further, bullet release pressure or friction has many more controlling variables than NT alone, such as inside neck smoothness, the presence of fouling in the neck, brushing, lubricants, brass properties, brass hardness, bullet construction, jacket materials, cold welding, etc, as well as length of neck reduction as Mikecr pointed out. I also agree that the way bullets exit the case is primarily by release of the bullet as the case neck and shoulder are blown out to chamber dimensions by combustion. Otherwise, as Mikecr mentioned in another post, the rifle would likely explode due to excessive pressure buildup. However, I think we can all agree that neck tension / bullet friction plays at least some effect in early pressure buildup and bullet release. If there was no interference or friction, the bullet would likely move even micron as pressure built prior to sufficient pressure building to expand the case neck. Even slight bullet movement will change case capacity and internal combustion dynamics. This is supported by countless findings over many years and many disciplines that have shown or reported differences in velocity, accuracy, and SD with only changes in NT. The question and source of controversy is how much of a role does NT play in this process. Is it so small as to be unmeasurable and/or statistically insignificant, or does it play a larger and more measurable role? This is where further studies and a different set of equipment will be required. I started out to answer one question regarding seating pressure differences between standard and Hammer bullets, and this morphed into curiosity about release pressures — whether truly relevant or not. However, I feel that some of the most interesting information found revolved around neck reduction, transition point of elastic to plastic deformation, maximum obtainable NT, and the role of mandrel use in obtaining maximum NT. Most importantly, I feel that there will be a maximum amount of neck reduction, after which additional NT will not be possible, and that anything over this amount will only serve to overwork brass and potentially damage bullets. The only other effectors that come into play are the length of neck reduced (as Mikecr suggested), and whether a mandrel is used to expand the neck to desired size as the last step, which appears to serve in creating additional inwardly directed elastic neck tension. Any additional bullet friction adding to release pressure increases will likely be achieved only by the variables mentioned above (inside neck smoothness, the presence of fouling in the neck, brushing, lubricants, brass properties, brass hardness, bullet construction, jacket materials, cold welding, etc). Again, the question returns to does this matter at all, and if so, how much. I believe that in the end, this will be shown to a measurable effect on accuracy, velocity, and precision. However, I believe the effect will be small in relation to other variables such as powder, bullets, primers, and barrels. These effects will likely only be fully realizable to those with highly accurate equipment and excellent technique. Further, I agree with Tiny Tim that there a significant number of variables contributing to the topics described above, as well as to accuracy in general — probably even more than we currently understand and can measure. To further complicate matters, all of these interacting events occur and influence each other in the course of milliseconds. I have no way of measuring pressure. However, I am curious as to how the above measurably affects accuracy, velocity, and precision, and this is something that can be done even if we can’t accurately measure the pieces of the puzzle or don’t fully understand the process. I plan to look into this further, but I would really like to have an AMP press so I can much more accurately and consistently measure seating and release variables to make the data more usable. It is too easy to over or under interpret data when the background noise is large. I would also like to add neck crimping to the test groups as I feel this will likely tease out additional info. Great discussion. Thanks, Mike D [/QUOTE]
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