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Long Range Hunting & Shooting
I am very dissapointed with Berger bullets regarding the 338 hybrid bullet.
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<blockquote data-quote="BryanLitz" data-source="post: 403116" data-attributes="member: 7848"><p>I've been away for a while and am just getting caught up with this thread again. I haven't read every word, but get the gist of what's being discussed and have some comments.</p><p></p><p>First, Eric was discussing the max acceleration in terms of G forces realized by the bullet to be around 800 G's. He left a zero off, it's closer to 80,000 to 100,000 G's of acceleration at the pressure spike. This is just academic, but quite astounding.</p><p></p><p>Next, the situations where the standard .338 LM was consistently producing nose slump involved the use of ball powders. Ball powders are typically faster burning and will produce a higher pressure spike for a given MV. Loading the .338 LM with slow burning stick powders like H1000 have not produced nose slump to my knowledge.</p><p></p><p>Regarding the freebore and seating depth effects on pressure/max pressure and velocity, the following is only my understanding and may not be entirely accurate. It's just how I 'think' it works.</p><p></p><p>First consider a 'smoothbore' situation, that is, remove the riflings from the barrel and just look at the effect that seating depth has on case capacity. In this case, I believe that loading the bullet out farther (increasing COAL) will reduce the peak pressure and MV. Reason is because the powder burn rate depends on pressure and heat. If the powder ignites in a smaller chamber, it's initial pressure will be higher, and the burn rate will reach a higher initial value, resulting higher peak pressure (it's a circular relationship). If the bullet is seated out farther (longer COAL), the initial pressure is lower and results in a lower initial burn rate and pressure spike.</p><p></p><p>Now consider what happens when the bullet encounters the riflings; which is, the bullet encounters a resistance to it's forward motion. This will cause the pressure behind the bullet to increase, thus increasing the burn rate, and in turn increasing the pressure even more. If you shoot the <u>same ammo</u> in 3 chambers, all having different lengths of free-bore, I would expect the chamber with the shortest free-bore to reach the highest max pressure. The reason is because if the bullet encounters resistance (hits the riflings) while the space behind the bullet is still small, then the burn rate and pressure will increase more rapidly and reach a higher value than if the bullet gets further down the barrel (leaving a greater, cooler, lower pressure volume behind).</p><p></p><p>What makes this so hard to correlate in reality is because we don't vary our throat length, we vary the seating depth, which is actually varying two variables at once. Then if you vary powder charge, it's a completely different dynamic. Seating a bullet deeper into the case (shorter COAL) increases initial pressure because the initial combustion chamber is smaller, HOWEVER, the shorter COAL also has the effect of reducing the chamber pressure because the bullet gets farther down the barrel before it encounters the riflings. Which of these offsetting factors is stronger? I don't know. Maybe some cartridge configurations and powder burn rates will cause one effect to be stronger than the other which would account for the conflicting observations above. I think the highest pressure situation you could have is a short freebore with the bullets loaded into the riflings with a near 100% fill ratio load. In that case, there's nothing to take the edge off the initial pressure spike.</p><p></p><p>Don't forget about the effect of neck tension. </p><p></p><p>Again the above is just my understanding of how it works and should not be considered 'authoritative'.</p><p></p><p>-Bryan</p></blockquote><p></p>
[QUOTE="BryanLitz, post: 403116, member: 7848"] I've been away for a while and am just getting caught up with this thread again. I haven't read every word, but get the gist of what's being discussed and have some comments. First, Eric was discussing the max acceleration in terms of G forces realized by the bullet to be around 800 G's. He left a zero off, it's closer to 80,000 to 100,000 G's of acceleration at the pressure spike. This is just academic, but quite astounding. Next, the situations where the standard .338 LM was consistently producing nose slump involved the use of ball powders. Ball powders are typically faster burning and will produce a higher pressure spike for a given MV. Loading the .338 LM with slow burning stick powders like H1000 have not produced nose slump to my knowledge. Regarding the freebore and seating depth effects on pressure/max pressure and velocity, the following is only my understanding and may not be entirely accurate. It's just how I 'think' it works. First consider a 'smoothbore' situation, that is, remove the riflings from the barrel and just look at the effect that seating depth has on case capacity. In this case, I believe that loading the bullet out farther (increasing COAL) will reduce the peak pressure and MV. Reason is because the powder burn rate depends on pressure and heat. If the powder ignites in a smaller chamber, it's initial pressure will be higher, and the burn rate will reach a higher initial value, resulting higher peak pressure (it's a circular relationship). If the bullet is seated out farther (longer COAL), the initial pressure is lower and results in a lower initial burn rate and pressure spike. Now consider what happens when the bullet encounters the riflings; which is, the bullet encounters a resistance to it's forward motion. This will cause the pressure behind the bullet to increase, thus increasing the burn rate, and in turn increasing the pressure even more. If you shoot the [U]same ammo[/U] in 3 chambers, all having different lengths of free-bore, I would expect the chamber with the shortest free-bore to reach the highest max pressure. The reason is because if the bullet encounters resistance (hits the riflings) while the space behind the bullet is still small, then the burn rate and pressure will increase more rapidly and reach a higher value than if the bullet gets further down the barrel (leaving a greater, cooler, lower pressure volume behind). What makes this so hard to correlate in reality is because we don't vary our throat length, we vary the seating depth, which is actually varying two variables at once. Then if you vary powder charge, it's a completely different dynamic. Seating a bullet deeper into the case (shorter COAL) increases initial pressure because the initial combustion chamber is smaller, HOWEVER, the shorter COAL also has the effect of reducing the chamber pressure because the bullet gets farther down the barrel before it encounters the riflings. Which of these offsetting factors is stronger? I don't know. Maybe some cartridge configurations and powder burn rates will cause one effect to be stronger than the other which would account for the conflicting observations above. I think the highest pressure situation you could have is a short freebore with the bullets loaded into the riflings with a near 100% fill ratio load. In that case, there's nothing to take the edge off the initial pressure spike. Don't forget about the effect of neck tension. Again the above is just my understanding of how it works and should not be considered 'authoritative'. -Bryan [/QUOTE]
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I am very dissapointed with Berger bullets regarding the 338 hybrid bullet.
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