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recoil v accuracy
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<blockquote data-quote="westcliffe01" data-source="post: 523242" data-attributes="member: 35183"><p><img src="http://varmintal.com/fullriflemovie16.gif" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>This was a finite element analysis run on a rifle action/barrel to understand what was going on. All the deformations are magnified many times so that even a layman can see what is going on. Varmint Al is a retired engineer.</p><p></p><p>Extract</p><p>"<strong>CONCLUSION....</strong> Maybe the "consensus" was that a rifle barrel vibrated in one or more of the mode shapes when fired. That was because the mode shapes and frequencies were easy to calculate and they did seem to answer some of the questions. From these FEA dynamic pressure calculations, it appears that the recoil and forced deformations are much more important than the natural vibration modes in determining where a barrel is pointing when the bullet exits the muzzle. Then after the bullet exits the muzzle, the rifle barrel vibrates in its various natural frequencies and mode shapes. Put another way, consider a guitar string being plucked. One pulls the string into a position (forced position) then releases it and the string vibrates at is natural frequency. The recoil and bullet motions "pulls" the rifle barrel to a new shape and once the bullet leaves the barrel, then the barrel vibrates. However, the addition of the scope to the model has shown some small high frequency vibrations superimposed on the forced deformations, both of which, slightly alter where the muzzle points before the bullet exits. For lowering the amplitude of the high frequency vibrations, it appears that even an "out of tune" tuner is better than no tuner at all. "</p><p></p><p>You can read his engineering page here: <a href="http://varmintal.com/aengr.htm" target="_blank">Varmint Al's Engineering Page - Finite Element Analysis of Structures</a></p><p></p><p>"Before retiring in 1990, I worked at the Lawrence Livermore National Lab for 30 years. The last few years I was the Advanced Engineering Analysis Group Leader in Weapons Engineering Division. We analyzed very complex structures. Physics developed the concepts and engineering made them deliverable. It was a great job and it was rewarding to help win the Cold War. Before becoming group leader, the last weapon system I worked on was the B-83."</p><p></p><p>Read the original article here : <a href="http://varmintal.com/amode.htm" target="_blank">Barrel Harmonics Mode Shape Movies</a></p><p></p><p>Final addition:</p><p></p><p>Here the force on the butt and fore end of the rifle were measured when weighed down with sandbags. This data fully refutes the claim that recoil begins when the bullet reaches the muzzle.</p><p></p><p>Note the force on the butt peak at about 112lb at about 0.6ms, long before the bullet has reached the muzzle. The fore end has lifted off the rest (was loaded 10lb) even before that.</p><p></p><p><img src="http://varmintal.com/6ppc-rest-loads-vs-time.png" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p></blockquote><p></p>
[QUOTE="westcliffe01, post: 523242, member: 35183"] [IMG]http://varmintal.com/fullriflemovie16.gif[/IMG] This was a finite element analysis run on a rifle action/barrel to understand what was going on. All the deformations are magnified many times so that even a layman can see what is going on. Varmint Al is a retired engineer. Extract "[B]CONCLUSION....[/B] Maybe the "consensus" was that a rifle barrel vibrated in one or more of the mode shapes when fired. That was because the mode shapes and frequencies were easy to calculate and they did seem to answer some of the questions. From these FEA dynamic pressure calculations, it appears that the recoil and forced deformations are much more important than the natural vibration modes in determining where a barrel is pointing when the bullet exits the muzzle. Then after the bullet exits the muzzle, the rifle barrel vibrates in its various natural frequencies and mode shapes. Put another way, consider a guitar string being plucked. One pulls the string into a position (forced position) then releases it and the string vibrates at is natural frequency. The recoil and bullet motions "pulls" the rifle barrel to a new shape and once the bullet leaves the barrel, then the barrel vibrates. However, the addition of the scope to the model has shown some small high frequency vibrations superimposed on the forced deformations, both of which, slightly alter where the muzzle points before the bullet exits. For lowering the amplitude of the high frequency vibrations, it appears that even an "out of tune" tuner is better than no tuner at all. " You can read his engineering page here: [URL="http://varmintal.com/aengr.htm"]Varmint Al's Engineering Page - Finite Element Analysis of Structures[/URL] "Before retiring in 1990, I worked at the Lawrence Livermore National Lab for 30 years. The last few years I was the Advanced Engineering Analysis Group Leader in Weapons Engineering Division. We analyzed very complex structures. Physics developed the concepts and engineering made them deliverable. It was a great job and it was rewarding to help win the Cold War. Before becoming group leader, the last weapon system I worked on was the B-83." Read the original article here : [URL="http://varmintal.com/amode.htm"]Barrel Harmonics Mode Shape Movies[/URL] Final addition: Here the force on the butt and fore end of the rifle were measured when weighed down with sandbags. This data fully refutes the claim that recoil begins when the bullet reaches the muzzle. Note the force on the butt peak at about 112lb at about 0.6ms, long before the bullet has reached the muzzle. The fore end has lifted off the rest (was loaded 10lb) even before that. [IMG]http://varmintal.com/6ppc-rest-loads-vs-time.png[/IMG] [/QUOTE]
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