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Old November 6, 2012, 03:58 PM   #25
Senior Member
Join Date: October 18, 2006
Posts: 7,030
Bart B.

To explain my comment.

Two powders that have the same barrel time may produce equally good groups with different muzzle velocities. Or they might not, but it is worth looking into.

During a load workup (Audette ladder, OCW, etc) you expect to find "accuracy nodes" with a given powder/bullet combination. I listed a few of the common ones.

Varmint Al should probably have a talk with Bill Calfee about how barrels actually vibrate. Because either one or both of them is wrong.

As far as the OBT paper goes, the author did not eliminate pressure variation timing as a cause of the variation that he proscribed to harmonics. He makes a good case for his idea, but when the shockwave traveling through steel is 5 to 8 times faster than the accellerating bullet, the "traveling wave" will have functionally traveled 8 to 10 barrel lengths by the time the bullet gets to the muzzle.

"Free Space Loss" of a traveling wave comes into play (the authors epiphany of guy wires transmitting a wave is stupid, there is no fixed point at the muzzle to reflect energy back towards the action), so the chart showing muzzle diameter verses time is misleading because each "expansion" must by less than the one before it (unless you get a secondary spike from the powder, as outlined here:

Now if the OBT method produces accurate ammo, by all means use it :-) Whether it is actually modeling the truth is another matter (one that makes me wish I had a few laser measuring devices to accurately map barrel movement during firing).

Machine guns are awesome until you have to carry one.
Jimro is offline  
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