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Rifles, Reloading, Optics, Equipment
Reloading
Known Loads too hot now..why
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<blockquote data-quote="bigngreen" data-source="post: 384843" data-attributes="member: 13632"><p><strong>What Happens When You Fire A Gun?</strong></p><p></p><p><strong><em>By M.L. McPherson</em></strong></p><p>©Copyright 2008, The Varmint Hunters Association, Inc.</p><p></p><p><strong>THE CASE</strong></p><p>"As the striker hits the primer, it drives the case forward in the chamber (to the extent that headspace will allow). On some cases with poor headspace control (e.g., 35 Whelen), the striker can drive the case into the chamber with enough force to move the shoulder back and thereby increase headspace.</p><p></p><p>As the primer pellet explodes, it generates considerable additional force that works to drive the case forward (and will do so, if headspace control is inadequate) and the primer backward (the primer moves until it is supported by the bolt). For cases using small primers, this force is about 750 pounds; for cases using large primers, this force is about 1,500 pounds (cases that have small-diameter flash holes generate greater force).</p><p></p><p>As the powder charge ignites and chamber pressure begins to build, the hollow portion of the case stretches, to fill the available space. When chamber pressure reaches approximately 3,000 psi, the case walls begin to push against the chamber. Thereafter, as pressure progressively increases, case-to-chamber bonding becomes progressively more solid.</p><p></p><p>When the force inside the case becomes sufficient, the case body yields and the case head begins to move rearward. The amount of pressure the case can withstand before the case head begins to move rearward depends upon case wall thickness and hardness (in the area near the body-to-web transition), difference between web diameter and primer pocket diameter, and how long pressure stays above the threshold pressure (where case begins to yield).</p><p></p><p>In most typical loads used in modern guns, chamber pressure will always be sufficient to drive the case head rearward and thereby stretch the case walls. Depending upon case wall thickness and degree of wall thickness taper near the body-to-web transition, the case can elastically stretch some amount — typically several thousandths inch. When this stretching exceeds the elastic limit for that case, the case walls will permanently thin and lengthen. This damage usually occurs about 0.1-inch forward of the floor of the case web.</p><p></p><p>After chamber pressure becomes sufficient to initiate case wall stretching, the case head soon hits the bolt. As pressure progressively increases, it pushes the case head progressively harder against the bolt. Hence, the bolt will progressively compress and the action will progressively stretch until chamber pressure peaks. (Actually, owing to inertia, the case head will continue to push against the bolt, as the bolt continues to retreat, for some time after chamber pressure has peaked."</p><p></p><p><span style="font-size: 12px">Now put some water between the case wall and the chamber and what will happen?</span> </p><p></p><p>Sounds like a good test, dunk the cartridge in water just a little smudge won't do for the sake of gloating why not rip off 3 shots. I suspect that if the chamber has a tight head space the effects may be smaller than a longer head spacing, again don't know just a thought.</p><p>Buffallobob brought it up first, hopefully he will weigh in with more experience with it.</p><p></p><p>Maybe we should start a Myth Busters thread instead of hijacking this one?</p></blockquote><p></p>
[QUOTE="bigngreen, post: 384843, member: 13632"] [B]What Happens When You Fire A Gun?[/B] [B][I]By M.L. McPherson[/I][/B] ©Copyright 2008, The Varmint Hunters Association, Inc. [B]THE CASE[/B] "As the striker hits the primer, it drives the case forward in the chamber (to the extent that headspace will allow). On some cases with poor headspace control (e.g., 35 Whelen), the striker can drive the case into the chamber with enough force to move the shoulder back and thereby increase headspace. As the primer pellet explodes, it generates considerable additional force that works to drive the case forward (and will do so, if headspace control is inadequate) and the primer backward (the primer moves until it is supported by the bolt). For cases using small primers, this force is about 750 pounds; for cases using large primers, this force is about 1,500 pounds (cases that have small-diameter flash holes generate greater force). As the powder charge ignites and chamber pressure begins to build, the hollow portion of the case stretches, to fill the available space. When chamber pressure reaches approximately 3,000 psi, the case walls begin to push against the chamber. Thereafter, as pressure progressively increases, case-to-chamber bonding becomes progressively more solid. When the force inside the case becomes sufficient, the case body yields and the case head begins to move rearward. The amount of pressure the case can withstand before the case head begins to move rearward depends upon case wall thickness and hardness (in the area near the body-to-web transition), difference between web diameter and primer pocket diameter, and how long pressure stays above the threshold pressure (where case begins to yield). In most typical loads used in modern guns, chamber pressure will always be sufficient to drive the case head rearward and thereby stretch the case walls. Depending upon case wall thickness and degree of wall thickness taper near the body-to-web transition, the case can elastically stretch some amount — typically several thousandths inch. When this stretching exceeds the elastic limit for that case, the case walls will permanently thin and lengthen. This damage usually occurs about 0.1-inch forward of the floor of the case web. After chamber pressure becomes sufficient to initiate case wall stretching, the case head soon hits the bolt. As pressure progressively increases, it pushes the case head progressively harder against the bolt. Hence, the bolt will progressively compress and the action will progressively stretch until chamber pressure peaks. (Actually, owing to inertia, the case head will continue to push against the bolt, as the bolt continues to retreat, for some time after chamber pressure has peaked." [SIZE=3]Now put some water between the case wall and the chamber and what will happen?[/SIZE] Sounds like a good test, dunk the cartridge in water just a little smudge won't do for the sake of gloating why not rip off 3 shots. I suspect that if the chamber has a tight head space the effects may be smaller than a longer head spacing, again don't know just a thought. Buffallobob brought it up first, hopefully he will weigh in with more experience with it. Maybe we should start a Myth Busters thread instead of hijacking this one? [/QUOTE]
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