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6mm Competition Match by MCR
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<blockquote data-quote="Kevin Cram" data-source="post: 677495" data-attributes="member: 2215"><p>The 6mm CM is not necessarily a new cartridge. I've found information on it from Joe Hendricks as far back as 2005 and I know he's been experimenting with other variations long before that . I'm not exactly sure what year he first chambered one in 6mm CM, but from 2005 to now it has finally gotten to the point where the rifles that were chambered in it have had the time to get 3500 - 4000 rounds through them and prove the longer barrel life. </p><p></p><p>Here's some quoted info from Joe Hendrick taken from the pdf attachment earlier in this thread.</p><p></p><p>What our research and experience has shown is that barrel life is directly related</p><p>to how much you push the cartridge. There is much we do not understand about</p><p>barrel life, but our experience has proven that what we are doing works and works</p><p>very well.</p><p>When you shoot a cartridge with less capacity you have to shoot faster burning</p><p>powder to obtain equal velocities to a cartridge of the same bullet diameter with a</p><p>larger capacity, or you are giving up velocity while still pushing the cartridge as</p><p>hard as you can. (6BR, 6mm-22-250, 6XC).</p><p>Shooting the faster burning powder does three things to your barrel.</p><p>1) First; the faster burning powder burns at a hotter temperature. Steel, what</p><p>all barrels are made from, is more malleable at higher temperatures. What</p><p>this means is that the hotter the temperature inside the barrel the more</p><p>metal that can be removed by the softer copper bullet. This is especially</p><p>important in rapid fire strings and during practice where there isn't as</p><p>much time between shots or strings. The difference in temperature from</p><p>the faster burning powders to the slower burning powders is minimal,</p><p>however over 2000 to 3000 rounds it does make a difference.</p><p>2) Second with the faster burning powder, the pressure behind the bullet goes</p><p>up very fast and goes down very fast. The maximum pressure of the shot</p><p>takes place very quickly in or around the throat area of the barrel. This</p><p>puts the maximum force on the most important part of the barrel. Anyone</p><p>who has ever bent a paper clip or wire back and forth understands that if</p><p>you do it enough the material weakens and eventually breaks. Faster</p><p>burning powder is doing this your barrel and overtime it weakens. This is</p><p>obviously a factor in barrel life.</p><p>3) Third faster burning powder burns faster and burns more in the throat of</p><p>your barrel. What this means is that the area where the bullet contacts the</p><p>lands of the barrel takes all of the abuse. Not just from the bullet, but from</p><p>the powder also.</p><p>What has been concluded from this is that faster burning powder stress the barrel</p><p>more than slower burning powder, by the force of the pressure, by the heat that</p><p>weakens the steel, and then by the burning of the powder.</p><p></p><p>The reasons for longer barrel life:</p><p>1) First the slower burning powder burns at a cooler temperature than faster</p><p>burning powders. These lower temperatures have a great affect on</p><p>extending barrel life. The barrel is not subject to as hot of a temperature</p><p>and therefore the bullets do not have as much of an affect on the steel as</p><p>with faster burning powders. The barrel's steel is less malleable because</p><p>of lower temperatures. You are not subjecting your barrel to the same</p><p>temperatures you do with faster burning powder. Keep in mind that the</p><p>temperature difference is minimal to you and I but to the barrel it is</p><p>making a huge difference.</p><p>2) Second the pressure curve is much different with a slower burning</p><p>powder. With a slower burning powder the pressure peak is down the</p><p>barrel much farther. The pressure curve is much smoother and even</p><p>though the peak pressure is about the same it stresses more of the length of</p><p>the barrel. What this means is that you are subjecting your barrel to a</p><p>lower average stress over the length of the barrel on every shot and the</p><p>stress is spread over a larger portion of the barrel's length. Again, think of</p><p>the paperclip, if you only bend it a little and bend it in different places it</p><p>takes much longer to break it. The lower pressure and the pressure applied</p><p>over a greater amount of the barrel adds to the life of the barrel.</p><p>3) Third, it burns slower. Therefore the powder is burning as it goes down</p><p>the barrel. However, we want as much of the powder to burn in the case</p><p>as possible and that is part of the design of the 6CM. The slower burning</p><p>powder gives a more even affect to the barrel. The burning powder is less</p><p>concentrated in one part of the barrel and barrel ware is more uniform.</p></blockquote><p></p>
[QUOTE="Kevin Cram, post: 677495, member: 2215"] The 6mm CM is not necessarily a new cartridge. I've found information on it from Joe Hendricks as far back as 2005 and I know he's been experimenting with other variations long before that . I'm not exactly sure what year he first chambered one in 6mm CM, but from 2005 to now it has finally gotten to the point where the rifles that were chambered in it have had the time to get 3500 - 4000 rounds through them and prove the longer barrel life. Here's some quoted info from Joe Hendrick taken from the pdf attachment earlier in this thread. What our research and experience has shown is that barrel life is directly related to how much you push the cartridge. There is much we do not understand about barrel life, but our experience has proven that what we are doing works and works very well. When you shoot a cartridge with less capacity you have to shoot faster burning powder to obtain equal velocities to a cartridge of the same bullet diameter with a larger capacity, or you are giving up velocity while still pushing the cartridge as hard as you can. (6BR, 6mm-22-250, 6XC). Shooting the faster burning powder does three things to your barrel. 1) First; the faster burning powder burns at a hotter temperature. Steel, what all barrels are made from, is more malleable at higher temperatures. What this means is that the hotter the temperature inside the barrel the more metal that can be removed by the softer copper bullet. This is especially important in rapid fire strings and during practice where there isn’t as much time between shots or strings. The difference in temperature from the faster burning powders to the slower burning powders is minimal, however over 2000 to 3000 rounds it does make a difference. 2) Second with the faster burning powder, the pressure behind the bullet goes up very fast and goes down very fast. The maximum pressure of the shot takes place very quickly in or around the throat area of the barrel. This puts the maximum force on the most important part of the barrel. Anyone who has ever bent a paper clip or wire back and forth understands that if you do it enough the material weakens and eventually breaks. Faster burning powder is doing this your barrel and overtime it weakens. This is obviously a factor in barrel life. 3) Third faster burning powder burns faster and burns more in the throat of your barrel. What this means is that the area where the bullet contacts the lands of the barrel takes all of the abuse. Not just from the bullet, but from the powder also. What has been concluded from this is that faster burning powder stress the barrel more than slower burning powder, by the force of the pressure, by the heat that weakens the steel, and then by the burning of the powder. The reasons for longer barrel life: 1) First the slower burning powder burns at a cooler temperature than faster burning powders. These lower temperatures have a great affect on extending barrel life. The barrel is not subject to as hot of a temperature and therefore the bullets do not have as much of an affect on the steel as with faster burning powders. The barrel’s steel is less malleable because of lower temperatures. You are not subjecting your barrel to the same temperatures you do with faster burning powder. Keep in mind that the temperature difference is minimal to you and I but to the barrel it is making a huge difference. 2) Second the pressure curve is much different with a slower burning powder. With a slower burning powder the pressure peak is down the barrel much farther. The pressure curve is much smoother and even though the peak pressure is about the same it stresses more of the length of the barrel. What this means is that you are subjecting your barrel to a lower average stress over the length of the barrel on every shot and the stress is spread over a larger portion of the barrel’s length. Again, think of the paperclip, if you only bend it a little and bend it in different places it takes much longer to break it. The lower pressure and the pressure applied over a greater amount of the barrel adds to the life of the barrel. 3) Third, it burns slower. Therefore the powder is burning as it goes down the barrel. However, we want as much of the powder to burn in the case as possible and that is part of the design of the 6CM. The slower burning powder gives a more even affect to the barrel. The burning powder is less concentrated in one part of the barrel and barrel ware is more uniform. [/QUOTE]
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