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Rifles, Reloading, Optics, Equipment
Gunsmithing
Lug setback? What am I missing?
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<blockquote data-quote="Johnny Jr." data-source="post: 1824217" data-attributes="member: 112651"><p>Mram10 us.... thanks for starting this thread. At first, I was dumbfounded that people were trying to say recoil has NOTHING to do with forces on the bolt. To me it was obvious that recoil from muzzle energy had to get to my shoulder mostly through the bolt lugs. I understood the pressure and cartridge head size formula to figure bolt forces....but certainly the foot pounds of energy causing recoil had to be a force ADDED to the bolt.....right?</p><p></p><p>I wanted to take exception to the Wiki article on bolt forces because it clearly only calculates PSI x inside case head diameter. It ignores energy related to recoil (bullet weight, speed, and mass of the gun powder).</p><p></p><p>I don't think Wiki is the arbiter of all truth in the universe, but I decided to NOT refute the formula that calculates bolt forces and then try to wrap my mind around how the recoil energy bypasses the lugs on its way to the gun butt.</p><p></p><p>The response to the Q and A in post #175 is what made the light bulb come on. My best attempt to explain it is: (And I'm not talking down to you because I know you know the basics as well or better than I did at the start) There is an equal and opposite reaction of the bullet mass being pushed through the barrel. The only thing the bullet has to push against on its way out is the grooves and lands of the tube it is in. So as the little mass is going one way, it's pushing back on the big mass. The tube is being shoved back into the receiver. The receiver is locked down to the stock by the recoil lug and action screws and in turn to your own body mass. So basically, that entire mass is pushing against the bullet........but here's the key (to me, anyway).....it's all going through the lands and grooves......not the bolt or lugs.</p><p></p><p>I completely agree with you that exaggerating the variables makes it easier to grasp. That's why I had such problem with the example of 8000 and 4300 ft lb in post 175 having the same bolt forces, yet NO recoil going through the bolt.</p><p></p><p>As a side note, my wife reminds me every day that I'm dumber than I think. But at least I learned something because you started this thread.Thanks.</p></blockquote><p></p>
[QUOTE="Johnny Jr., post: 1824217, member: 112651"] Mram10 us.... thanks for starting this thread. At first, I was dumbfounded that people were trying to say recoil has NOTHING to do with forces on the bolt. To me it was obvious that recoil from muzzle energy had to get to my shoulder mostly through the bolt lugs. I understood the pressure and cartridge head size formula to figure bolt forces....but certainly the foot pounds of energy causing recoil had to be a force ADDED to the bolt.....right? I wanted to take exception to the Wiki article on bolt forces because it clearly only calculates PSI x inside case head diameter. It ignores energy related to recoil (bullet weight, speed, and mass of the gun powder). I don't think Wiki is the arbiter of all truth in the universe, but I decided to NOT refute the formula that calculates bolt forces and then try to wrap my mind around how the recoil energy bypasses the lugs on its way to the gun butt. The response to the Q and A in post #175 is what made the light bulb come on. My best attempt to explain it is: (And I’m not talking down to you because I know you know the basics as well or better than I did at the start) There is an equal and opposite reaction of the bullet mass being pushed through the barrel. The only thing the bullet has to push against on its way out is the grooves and lands of the tube it is in. So as the little mass is going one way, it’s pushing back on the big mass. The tube is being shoved back into the receiver. The receiver is locked down to the stock by the recoil lug and action screws and in turn to your own body mass. So basically, that entire mass is pushing against the bullet........but here’s the key (to me, anyway).....it’s all going through the lands and grooves......not the bolt or lugs. I completely agree with you that exaggerating the variables makes it easier to grasp. That’s why I had such problem with the example of 8000 and 4300 ft lb in post 175 having the same bolt forces, yet NO recoil going through the bolt. As a side note, my wife reminds me every day that I’m dumber than I think. But at least I learned something because you started this thread.Thanks. [/QUOTE]
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Lug setback? What am I missing?
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