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Rifles, Reloading, Optics, Equipment
Gunsmithing
Lug setback? What am I missing?
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<blockquote data-quote="Gcan" data-source="post: 1821239" data-attributes="member: 102867"><p>If Kirby says he believes it, I don't necessarily have to fully understand it to accept it. Kinda like brain surgery. In this case he is 100% correct.</p><p></p><p>I could make several arguments but Clearly the lager bolt face puts more pressure into the lugs and abutments.</p><p></p><p></p><p>we all think in terms of equal chamber pressure being equal and that is deceiving.</p><p></p><p>simply put, if you know anything about air cylinders then Ill use 125 psi in this example. Two cylinders.</p><p></p><p>1" piston @ 125psi = .7845 sq/in x 125lbs = 98 lbs force on piston.</p><p></p><p>4" piston @ 125 psi = 12.466 sq/in x 125 lbs = 1558 lbs of force on piston.</p><p></p><p>Both pistons are operating at 125psi.</p><p></p><p>Now do the same equations for a 223 at 63,000 psi and a 338 at 63,000 and remember the bolt OD may be identical</p><p></p><p>Now consider the added thrust on:</p><p></p><p>The web thickness between the face and the end of the firing pin might be a factor. After all, regardless of the lug size, its whats under them that matters most. Then you have the same size or larger extractor as cases size increases. So in the same bolt body diameter, as case size increases the bolt face/lug area becomes proportionally weaker when, in a perfect world we would want the bolt to be proportionally bigger. </p><p></p><p>simply put: a 6mm anything at 63,000 psi does not put nearly the same pressure on bolt lugs that an edge or LM might at same chamber pressure.</p></blockquote><p></p>
[QUOTE="Gcan, post: 1821239, member: 102867"] If Kirby says he believes it, I don’t necessarily have to fully understand it to accept it. Kinda like brain surgery. In this case he is 100% correct. I could make several arguments but Clearly the lager bolt face puts more pressure into the lugs and abutments. we all think in terms of equal chamber pressure being equal and that is deceiving. simply put, if you know anything about air cylinders then Ill use 125 psi in this example. Two cylinders. 1” piston @ 125psi = .7845 sq/in x 125lbs = 98 lbs force on piston. 4” piston @ 125 psi = 12.466 sq/in x 125 lbs = 1558 lbs of force on piston. Both pistons are operating at 125psi. Now do the same equations for a 223 at 63,000 psi and a 338 at 63,000 and remember the bolt OD may be identical Now consider the added thrust on: The web thickness between the face and the end of the firing pin might be a factor. After all, regardless of the lug size, its whats under them that matters most. Then you have the same size or larger extractor as cases size increases. So in the same bolt body diameter, as case size increases the bolt face/lug area becomes proportionally weaker when, in a perfect world we would want the bolt to be proportionally bigger. simply put: a 6mm anything at 63,000 psi does not put nearly the same pressure on bolt lugs that an edge or LM might at same chamber pressure. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Gunsmithing
Lug setback? What am I missing?
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