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Rifles, Reloading, Optics, Equipment
Gunsmithing
Thoughts from the pro's
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<blockquote data-quote="Susquatch" data-source="post: 1624798" data-attributes="member: 31264"><p>Thanks for clarifying. It is indeed a great topic for conversation & even debate. Maybe your dad is my generation and got some of his thinking from magazine articles that were our only source of info before such things as the internet, forums, and websites existed.....</p><p></p><p>I am an engineer and a machinist and I am obsessed with science and the question "Why?". I'm not satisfied just knowing something works, or "that's the way we always do it". That's why I liked your question so much and took the liberty of attempting to rephrase it.</p><p></p><p>It is my personal belief that accuracy is all about the fidelity of repeatability. In other words, if everything happens exactly the same every time, then the bullet should go through the same hole. If we hold the rifle exactly the same, pull the trigger exactly the same, the sear releases exactly the same, firing pin springs forward exactly the same hitting the primer exactly the same way, primer ignites exactly the same with the same timing and force, powder ignites and burns in a precisely repeatable progression, bullet and case are aligned to the bore exactly the same way and leap forward engaging the leade and accelerating forward down the barrel with exactly the same geometry and timing, the brass slides rearward engaging the bolt face and sealing off the chamber exactly the same with rifle recoil movement in our arms and rests exactly the same, and bullet exits the crown exactly the same, all given exactly the same bullet weight, geometry, and balance, and external conditions, then the result is one hole in the target.</p><p></p><p>Of course, many things conspire and collaborate to upset this beautiful progression of precise repetition. The goal is to build a perfect rifle, perfect loads, and perfect our shooting skills that all can constrain the differences that work against this repeatability.</p><p></p><p>With all that hot air behind me, I would like once more to focus on your question. Assuming that this theory and my understanding of it is correct, then why would concentric alignment of threads be more or less important than the alignment of the bolt raceway? If the theory is correct, then misalignment doesn't matter at all - provided that the misalignment is consistent and exactly repeatable, it shouldn't matter one iota!</p><p></p><p>Harold Vaugn's work on such things (see his book "Rifle Accuracy Facts") answered some of these questions but in the process raised more questions than answers. Building on his work, I think the answer to this question (if it can be answered) lies in the precision of these respective alignments and their contribution to overall repeatabity through stress in the components (hysteresis in the movements of the parts and their initial conditions before and after the shot) and the precision of the fit of mating components.</p><p></p><p>In my fragile mind, it does not take a huge leap of faith to see that its much better to use the raceway as a reference for all subsequent efforts to achieve precision than it is to use the threads simply because the raceway is longer than the thread length which results in better overall precision through a more precise reference for that work. Think of it a bit like using a 001 dial gauge to zero concentricity vs a 0001 gauge. The 0001 gauge is ten times finer than the 001 and the bolt raceway is roughly ten times longer than the length of the threads.</p><p></p><p>I think it's also fair to say that it's a lot easier to true the threads to the raceway than it is to true the raceway to the threads.....</p><p></p><p>Does it really matter? I don't think so. As long as either approach has the same final result in the precision of the fit and resulting stresses that affect repeatability, I don't think either one is any better or more important than the other in the end result. But the devil is in the details. Achieving equal precision is MUCH easier using the raceway so that's what most of us do.</p><p></p><p>That said, those old timers who used lapping compound instead of a lathe achieved good results despite themselves for the same reason. At that time it was much easier to improve precision by lapping to improve the fit than it was to use a lathe that had babbit bearings and crappy precision. In fact, I don't remember seeing any 0001 indicators back in those days! I do remember wobble wires though..... LOL!</p><p></p><p>As you can see, you touched a nerve with your question. Precision and repeatability are subjects I think about quite often when I am figuring out why a given rifle doesn't shoot to its potential..</p><p></p><p>Sorry to be so long winded. It's a major flaw in my neural networks. I do hope my thoughts help further yours.</p></blockquote><p></p>
[QUOTE="Susquatch, post: 1624798, member: 31264"] Thanks for clarifying. It is indeed a great topic for conversation & even debate. Maybe your dad is my generation and got some of his thinking from magazine articles that were our only source of info before such things as the internet, forums, and websites existed..... I am an engineer and a machinist and I am obsessed with science and the question "Why?". I'm not satisfied just knowing something works, or "that's the way we always do it". That's why I liked your question so much and took the liberty of attempting to rephrase it. It is my personal belief that accuracy is all about the fidelity of repeatability. In other words, if everything happens exactly the same every time, then the bullet should go through the same hole. If we hold the rifle exactly the same, pull the trigger exactly the same, the sear releases exactly the same, firing pin springs forward exactly the same hitting the primer exactly the same way, primer ignites exactly the same with the same timing and force, powder ignites and burns in a precisely repeatable progression, bullet and case are aligned to the bore exactly the same way and leap forward engaging the leade and accelerating forward down the barrel with exactly the same geometry and timing, the brass slides rearward engaging the bolt face and sealing off the chamber exactly the same with rifle recoil movement in our arms and rests exactly the same, and bullet exits the crown exactly the same, all given exactly the same bullet weight, geometry, and balance, and external conditions, then the result is one hole in the target. Of course, many things conspire and collaborate to upset this beautiful progression of precise repetition. The goal is to build a perfect rifle, perfect loads, and perfect our shooting skills that all can constrain the differences that work against this repeatability. With all that hot air behind me, I would like once more to focus on your question. Assuming that this theory and my understanding of it is correct, then why would concentric alignment of threads be more or less important than the alignment of the bolt raceway? If the theory is correct, then misalignment doesn't matter at all - provided that the misalignment is consistent and exactly repeatable, it shouldn't matter one iota! Harold Vaugn's work on such things (see his book "Rifle Accuracy Facts") answered some of these questions but in the process raised more questions than answers. Building on his work, I think the answer to this question (if it can be answered) lies in the precision of these respective alignments and their contribution to overall repeatabity through stress in the components (hysteresis in the movements of the parts and their initial conditions before and after the shot) and the precision of the fit of mating components. In my fragile mind, it does not take a huge leap of faith to see that its much better to use the raceway as a reference for all subsequent efforts to achieve precision than it is to use the threads simply because the raceway is longer than the thread length which results in better overall precision through a more precise reference for that work. Think of it a bit like using a 001 dial gauge to zero concentricity vs a 0001 gauge. The 0001 gauge is ten times finer than the 001 and the bolt raceway is roughly ten times longer than the length of the threads. I think it's also fair to say that it's a lot easier to true the threads to the raceway than it is to true the raceway to the threads..... Does it really matter? I don't think so. As long as either approach has the same final result in the precision of the fit and resulting stresses that affect repeatability, I don't think either one is any better or more important than the other in the end result. But the devil is in the details. Achieving equal precision is MUCH easier using the raceway so that's what most of us do. That said, those old timers who used lapping compound instead of a lathe achieved good results despite themselves for the same reason. At that time it was much easier to improve precision by lapping to improve the fit than it was to use a lathe that had babbit bearings and crappy precision. In fact, I don't remember seeing any 0001 indicators back in those days! I do remember wobble wires though..... LOL! As you can see, you touched a nerve with your question. Precision and repeatability are subjects I think about quite often when I am figuring out why a given rifle doesn't shoot to its potential.. Sorry to be so long winded. It's a major flaw in my neural networks. I do hope my thoughts help further yours. [/QUOTE]
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