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223 Ackley Improved
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<blockquote data-quote="Fiftydriver" data-source="post: 121879" data-attributes="member: 10"><p>Coyote,</p><p></p><p>Not trying to start a flame here but seating the bullets into the lands will not control headspace effectively. The reason is because it takes very little chamber pressure to start the bullet into the bore, even the primer blast with a high load density will get the bullet started into the rifling. </p><p></p><p>The bullet will be well into the lands by the time that the pressure in the chamber has gotten high enough to expand the case in any way so when your firing pin hits your primer, it will drive the round forward until the shoulder of the case stops against the chamber. The primer may well ignite while the case is moving forward but the case will not be stopped by the bullet hitting the lands.</p><p></p><p>When the powder begins to ignite the bullet will be driven into the lands and down the bore with only minumul chamber pressure. THen as pressure builds in the chamber to the point where the case will expand to fill the chamber the bullet is well down the bore and away from the case.</p><p></p><p>As the pressure continues to build to top pressures, the case head is then slammed back until it is stopped by the bolt face, you will still get case head stretching.</p><p></p><p>I also wonder if you are actually getting case head seperation or if you are seeing a pressure buldge on the case just ahead of the web.</p><p></p><p>Nominal case head diameter for the 308 and '06 class of rounds is 0.470". Unfortunately there is not a US brass maker that makes brass much larger then 0.465" in diameter. As such, unless your gunsmith designed the chamber properly you will get a pressure buldge on the case just ahead of the solid case web. This will generally be more apparent on one side of the case or the other. </p><p></p><p>This is not case head seperation in any way but instead, just the case expanding where it can to fill an oversized chamber.</p><p></p><p>If you are actually getting case head seperation, there is an easy fix in the 243 AI. Use 260 Rem cases, neck them down until they will JUST chamber with slight pressure on the bolt. THis works because there will be a secondary shoulder on the 260 Rem case when necked down to 243 and that will act as the control on headspace. This depends on how loose your neck is though. In some cases you will need to go up to the 7mm-08 brass and do the same thing necking it down.</p><p></p><p>Make sure that your case necks are not to thick though.</p><p></p><p>If you are actually getting some case head seperation on the fireforming loads, if you only partial FL size from there out you will still get good chambering ammo and you will also have very little case head stretching from that point on as long as you do not oversize.</p><p></p><p>Again, seating the bullets into the lands is a very inefficent way to try to stop case head stretching. Only means that the chamber was not cut to the correct depth for an AI chamber.</p><p></p><p>Kirby Allen(50)</p></blockquote><p></p>
[QUOTE="Fiftydriver, post: 121879, member: 10"] Coyote, Not trying to start a flame here but seating the bullets into the lands will not control headspace effectively. The reason is because it takes very little chamber pressure to start the bullet into the bore, even the primer blast with a high load density will get the bullet started into the rifling. The bullet will be well into the lands by the time that the pressure in the chamber has gotten high enough to expand the case in any way so when your firing pin hits your primer, it will drive the round forward until the shoulder of the case stops against the chamber. The primer may well ignite while the case is moving forward but the case will not be stopped by the bullet hitting the lands. When the powder begins to ignite the bullet will be driven into the lands and down the bore with only minumul chamber pressure. THen as pressure builds in the chamber to the point where the case will expand to fill the chamber the bullet is well down the bore and away from the case. As the pressure continues to build to top pressures, the case head is then slammed back until it is stopped by the bolt face, you will still get case head stretching. I also wonder if you are actually getting case head seperation or if you are seeing a pressure buldge on the case just ahead of the web. Nominal case head diameter for the 308 and '06 class of rounds is 0.470". Unfortunately there is not a US brass maker that makes brass much larger then 0.465" in diameter. As such, unless your gunsmith designed the chamber properly you will get a pressure buldge on the case just ahead of the solid case web. This will generally be more apparent on one side of the case or the other. This is not case head seperation in any way but instead, just the case expanding where it can to fill an oversized chamber. If you are actually getting case head seperation, there is an easy fix in the 243 AI. Use 260 Rem cases, neck them down until they will JUST chamber with slight pressure on the bolt. THis works because there will be a secondary shoulder on the 260 Rem case when necked down to 243 and that will act as the control on headspace. This depends on how loose your neck is though. In some cases you will need to go up to the 7mm-08 brass and do the same thing necking it down. Make sure that your case necks are not to thick though. If you are actually getting some case head seperation on the fireforming loads, if you only partial FL size from there out you will still get good chambering ammo and you will also have very little case head stretching from that point on as long as you do not oversize. Again, seating the bullets into the lands is a very inefficent way to try to stop case head stretching. Only means that the chamber was not cut to the correct depth for an AI chamber. Kirby Allen(50) [/QUOTE]
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