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Rifles, Reloading, Optics, Equipment
Gunsmithing
Lug setback? What am I missing?
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<blockquote data-quote="bigedp51" data-source="post: 1821203" data-attributes="member: 28965"><p>You do not measure the outside diameter of the case or its rim diameter to figure the force on the bolt face. Meaning it is the inside diameter of the case that exerts the force on the bolt face just like a hydraulic piston.</p><p></p><p>And any lube or oil in the chamber increases bolt thrust because the case is not gripping the chamber walls. Meaning a dry chamber and cartridge reduces the bolt thrust and this varies with the yield strength of the brass.</p><p></p><p>My 30-30 at 38,000 cup or 43,000 psi always has protruding primers because the chamber pressure is not great enough to make the case stretch to meet the bolt face. Meaning you can't use the math formula because only the primer contacts the bolt face.</p><p></p><p><span style="font-size: 15px">Cartridge Pressure Standards</span></p><p><span style="font-size: 15px"><a href="http://kwk.us/pressures.html" target="_blank">http://kwk.us/pressures.html</a></span></p><p></p><p>The British used the base crusher system of measuring chamber pressure and the copper crusher was located on the base of the case. And with this system, the cases had to be oiled to measure actual chamber pressure. Below is from the British 1929 Textbook of Small Arms. In this same book the Enfield rifle was proof tested using two oiled proof cartridges and if the headspace increased .003 or more the rifle failed proof testing due to lug setback.</p><p></p><p><img src="https://i.imgur.com/W8oz09S.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>Bottom line, the brass cartridge case acts like a cars shock absorber and effects the amount of force and its dwell time on the bolt thrust. Meaning the math formula being used to figure the bolt thrust is "ball park" depending on other factors.</p><p></p><p>And this is just like P.O. Ackley's experiment when he removed the locking bolt from his 30-30 and remotely fired the rifle and nothing happened. The case gripped the chamber walls and only the primer contacted the bolt face.</p><p></p><p>And yes larger diameter cases do exert more force on the bolt face but there is more to bolt thrust than a ball park math formula.</p><p></p><p>Below is from the H.P. White Laboratories.</p><p></p><p> <img src="https://i.imgur.com/eWiBhrF.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p></blockquote><p></p>
[QUOTE="bigedp51, post: 1821203, member: 28965"] You do not measure the outside diameter of the case or its rim diameter to figure the force on the bolt face. Meaning it is the inside diameter of the case that exerts the force on the bolt face just like a hydraulic piston. And any lube or oil in the chamber increases bolt thrust because the case is not gripping the chamber walls. Meaning a dry chamber and cartridge reduces the bolt thrust and this varies with the yield strength of the brass. My 30-30 at 38,000 cup or 43,000 psi always has protruding primers because the chamber pressure is not great enough to make the case stretch to meet the bolt face. Meaning you can't use the math formula because only the primer contacts the bolt face. [SIZE=4]Cartridge Pressure Standards [URL]http://kwk.us/pressures.html[/URL][/SIZE] The British used the base crusher system of measuring chamber pressure and the copper crusher was located on the base of the case. And with this system, the cases had to be oiled to measure actual chamber pressure. Below is from the British 1929 Textbook of Small Arms. In this same book the Enfield rifle was proof tested using two oiled proof cartridges and if the headspace increased .003 or more the rifle failed proof testing due to lug setback. [IMG]https://i.imgur.com/W8oz09S.jpg[/IMG] Bottom line, the brass cartridge case acts like a cars shock absorber and effects the amount of force and its dwell time on the bolt thrust. Meaning the math formula being used to figure the bolt thrust is "ball park" depending on other factors. And this is just like P.O. Ackley's experiment when he removed the locking bolt from his 30-30 and remotely fired the rifle and nothing happened. The case gripped the chamber walls and only the primer contacted the bolt face. And yes larger diameter cases do exert more force on the bolt face but there is more to bolt thrust than a ball park math formula. Below is from the H.P. White Laboratories. [img]https://i.imgur.com/eWiBhrF.jpg[/img] [/QUOTE]
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Lug setback? What am I missing?
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