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Rifles, Reloading, Optics, Equipment
Reloading
My HBN experience and process
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<blockquote data-quote="QuietTexan" data-source="post: 2913066" data-attributes="member: 116181"><p>I get where you're going here and I agree with the general direction. But I'm not sure the last part is worded precisely enough to say I agree fully.</p><p></p><p>In this instance there would be a reduction in PEAK chamber pressure, but the result is a flattened curve and not a decrease in total amount of gas expansion if the mass of propellant is constant. Figuring the integral of each pressure curve might be a shortcut to confirm, but the total amount of work done by a fixed mass of propellant in the same sized pressure vessel should be the same even with a lower peak pressure. So yes PEAK pressure is reduced but that doesn't translate to loss of velocity. That can be proved with AI cartridges netting same velocities with essentially same charge weights at lower peak chamber pressures. AIs would require a very small amount of additional propellant mass to make up for the increase in volume of the chamber, but chamber dimensions don't change with HBN treatment to that doesn't apply here.</p><p></p><p>Work is Force x Displacement (barrel length is constant), and Force is Mass (bullet weight is constant) X Acceleration, so work should vary directly with acceleration since the other two values are constants in our case.</p><p></p><p>If HBN reduces friction it should result in something between faster acceleration and same acceleration with less friction, aka heat loss to the metal barrel. The amount of work done in a coated bore either increases, or at most doesn't change. I don't see a case where the amount of work decreases, netting a lower velocity at a constant charge weight. Work would increase if there's higher acceleration and/or less heat loss, or not change if increased acceleration results in increased parasitic loss relative to the baseline and they cancel each other out. But less friction, same acceleration, same amount of gas volume (or ideally less friction, more acceleration, same gas volume) should result in higher total work .</p><p></p><p>A shorter way to look at this might be that since heat loss from friction is a loss to outside the system, any reduction in friction effectively results in less parasitic loss, thus a higher total energy budget in the system even with the same propellant mass.</p><p></p><p>Admittedly what I said is not accounting for decrease in propellent burn velocity at lower pressure, I'm making the assumption the same amount of propellant mass is converted to gas in both case. This should be an accurate assumption in a high-power centerfire case, but would not be in a low-pressure case like 458 SOCOM where the bore volume is a significant enough factor to affect the completeness of powder burn pretty drastically. I've seen it in 300 BLK subs because of small case capacity/charge weight relative to bore size. But high-pressure cartridges should have a relatively consistent burn completeness percentage in the top 1/3rd of the pressure range.</p><p></p><p></p><p>This I do agree with, and is also part of the logic behind Shawn Carlock's +P throat design. Reducing peak chamber pressure allows you to run more propellant to get back to the same peak pressure, netting a higher average pressure compared to the original throat design. That logic should be the same for a HBN treated bore.</p></blockquote><p></p>
[QUOTE="QuietTexan, post: 2913066, member: 116181"] I get where you're going here and I agree with the general direction. But I'm not sure the last part is worded precisely enough to say I agree fully. In this instance there would be a reduction in PEAK chamber pressure, but the result is a flattened curve and not a decrease in total amount of gas expansion if the mass of propellant is constant. Figuring the integral of each pressure curve might be a shortcut to confirm, but the total amount of work done by a fixed mass of propellant in the same sized pressure vessel should be the same even with a lower peak pressure. So yes PEAK pressure is reduced but that doesn't translate to loss of velocity. That can be proved with AI cartridges netting same velocities with essentially same charge weights at lower peak chamber pressures. AIs would require a very small amount of additional propellant mass to make up for the increase in volume of the chamber, but chamber dimensions don't change with HBN treatment to that doesn't apply here. Work is Force x Displacement (barrel length is constant), and Force is Mass (bullet weight is constant) X Acceleration, so work should vary directly with acceleration since the other two values are constants in our case. If HBN reduces friction it should result in something between faster acceleration and same acceleration with less friction, aka heat loss to the metal barrel. The amount of work done in a coated bore either increases, or at most doesn't change. I don't see a case where the amount of work decreases, netting a lower velocity at a constant charge weight. Work would increase if there's higher acceleration and/or less heat loss, or not change if increased acceleration results in increased parasitic loss relative to the baseline and they cancel each other out. But less friction, same acceleration, same amount of gas volume (or ideally less friction, more acceleration, same gas volume) should result in higher total work . A shorter way to look at this might be that since heat loss from friction is a loss to outside the system, any reduction in friction effectively results in less parasitic loss, thus a higher total energy budget in the system even with the same propellant mass. Admittedly what I said is not accounting for decrease in propellent burn velocity at lower pressure, I'm making the assumption the same amount of propellant mass is converted to gas in both case. This should be an accurate assumption in a high-power centerfire case, but would not be in a low-pressure case like 458 SOCOM where the bore volume is a significant enough factor to affect the completeness of powder burn pretty drastically. I've seen it in 300 BLK subs because of small case capacity/charge weight relative to bore size. But high-pressure cartridges should have a relatively consistent burn completeness percentage in the top 1/3rd of the pressure range. This I do agree with, and is also part of the logic behind Shawn Carlock's +P throat design. Reducing peak chamber pressure allows you to run more propellant to get back to the same peak pressure, netting a higher average pressure compared to the original throat design. That logic should be the same for a HBN treated bore. [/QUOTE]
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