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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Overbore Index Chart & 26 Nosler
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<blockquote data-quote="J E Custom" data-source="post: 965145" data-attributes="member: 2736"><p>I am by no means a expert on this subject and have read every article I could to understand the relationship between a case/cartridge and barrel life. PO Ackley was one of the first to address this </p><p>and do extensive testing to understand this issue.</p><p></p><p>His writings are very well known and tested/proven so he is one resource that I truly believe. With that said, Hear is the way I understand all of this.</p><p></p><p>First he states that there are no ONE formula for deciding barrel life based on case capacity compared to bullet diameter.</p><p></p><p>There are to many variables effecting barrel life.</p><p></p><p>There are at least 6 different factors that effect barrel life and determine what is considered </p><p>"Overbore"</p><p></p><p>Type of powder, bore grove diameter, twist rate (Pitch) sectional density of bullet, allowable</p><p>pressure and case shape. </p><p></p><p>The shape of the case will have a large effect on erosion even though they have the same volume.</p><p>In his writings he states that he found that the longer cases with lots of body taper caused the powder to have different burn characteristics that the short straight body cases with the same volume forcing the powder to compress and be pushed through the neck causing more throat erosion from the un-burnt powder. The short straight sided cases burned more powder before it left the case with the same amount of powder because of the shorter column of powder and the greater shoulder angle. (30 to 40%) that don't compress the powder and force as much out of the barrel before it is burned.</p><p></p><p>He also addressed the effects of twist rates on barrel erosion. Using the same cartridge, volume, </p><p>bullet weight in barrels of the same length, but with different twist he discovered that 30 to 35 %</p><p>of the energy needed to push the bullet down the barrel was used to rotate the bullet depending </p><p>on the twist rate. To prove this they tested a barrel with No twist (Smooth Bore) trying to get 100% on the energy to propel the bullet. The smooth bore did get more velocity but lost accuracy. So a fast twist barrel will need more powder/pressure to get the same velocity as a slow pitch barrel of the same case capacity and powder charge. </p><p></p><p>What all of this tells me is that some cartridges may not be over bored but can still decrease barrel</p><p>life, and some of the large "Over bored" cartridges may not be as bad as though because of there case design, the type of powder used, the type of bullet, the twist rate ETC.</p><p></p><p>With all of this, I don't worry about barrel life and just plan on a barrel change when and if it needs one.</p><p></p><p>There is a lot more information available and one should read as much as possible to understand</p><p>the effects of all factors and decide which way to go.</p><p></p><p>Conclusion = The 26 Nosler may very well be a reasonable barrel burner and based on the information available there are worse barrel burner cartridges in use.</p><p></p><p>Don't let it get Hot, keep it clean and don't over load it and you should get reasonable or good barrel life with it.</p><p></p><p>J E CUSTOM</p></blockquote><p></p>
[QUOTE="J E Custom, post: 965145, member: 2736"] I am by no means a expert on this subject and have read every article I could to understand the relationship between a case/cartridge and barrel life. PO Ackley was one of the first to address this and do extensive testing to understand this issue. His writings are very well known and tested/proven so he is one resource that I truly believe. With that said, Hear is the way I understand all of this. First he states that there are no ONE formula for deciding barrel life based on case capacity compared to bullet diameter. There are to many variables effecting barrel life. There are at least 6 different factors that effect barrel life and determine what is considered "Overbore" Type of powder, bore grove diameter, twist rate (Pitch) sectional density of bullet, allowable pressure and case shape. The shape of the case will have a large effect on erosion even though they have the same volume. In his writings he states that he found that the longer cases with lots of body taper caused the powder to have different burn characteristics that the short straight body cases with the same volume forcing the powder to compress and be pushed through the neck causing more throat erosion from the un-burnt powder. The short straight sided cases burned more powder before it left the case with the same amount of powder because of the shorter column of powder and the greater shoulder angle. (30 to 40%) that don't compress the powder and force as much out of the barrel before it is burned. He also addressed the effects of twist rates on barrel erosion. Using the same cartridge, volume, bullet weight in barrels of the same length, but with different twist he discovered that 30 to 35 % of the energy needed to push the bullet down the barrel was used to rotate the bullet depending on the twist rate. To prove this they tested a barrel with No twist (Smooth Bore) trying to get 100% on the energy to propel the bullet. The smooth bore did get more velocity but lost accuracy. So a fast twist barrel will need more powder/pressure to get the same velocity as a slow pitch barrel of the same case capacity and powder charge. What all of this tells me is that some cartridges may not be over bored but can still decrease barrel life, and some of the large "Over bored" cartridges may not be as bad as though because of there case design, the type of powder used, the type of bullet, the twist rate ETC. With all of this, I don't worry about barrel life and just plan on a barrel change when and if it needs one. There is a lot more information available and one should read as much as possible to understand the effects of all factors and decide which way to go. Conclusion = The 26 Nosler may very well be a reasonable barrel burner and based on the information available there are worse barrel burner cartridges in use. Don't let it get Hot, keep it clean and don't over load it and you should get reasonable or good barrel life with it. J E CUSTOM [/QUOTE]
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Overbore Index Chart & 26 Nosler
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