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jacket thickness differences as well as different harmonics. The barrel vibrates in the shape of the infinty symbol. the best groups are acheived when the bullet exits the muzzle at the intersection, however, a bullet/load may exit the muzzle at a different point, but do it consistently at the same point, and will show accuracy as well.
Jacket thickness coupled with a different "dwell" time than the v-max.
my .002"
Jacket thickness has no "bearing"( /ubbthreads/images/graemlins/smile.gif )on this. Where does this crap come from??
The vibrations in a barrel ("IF" it has them) do not form an infinity pattern - they are random, and they vary with different barrels, and are so slow that they cannot complete a single cycle before the bullet leaves the muzzle.
The "resonant frequency" of a barrel is only a hundred or so whips per second - the "dwell time" in the barrel of a high speed bullet is 1.5 to 2 milliseconds. So a "Dwell cycle" takes 10 milliseconds, the bullet is gone in 1/5th of a single cycle - in other words - if the barrel "is" harmonically vibration, the bullet is gone before 1/5th of the first cycle has started...
... do the math yourself!
.
jacket thickness i.e.(overall dia) and or a difference in jacket density/material will affect pressure. This is a very provable fact since some benchrest barrels won't shoot a J4 jacketed bullet and others won't shoot anything but a J4 jacketed bullet. I have some barrels that will fling a berger bullet into patterns, and others that will bughole them. The gunsmith told me that is just the way of things. Some rifling lands are higher, some are shallower, even in barrels from the same maker. It depends on the barrel itself, and the barrel dictates the jacket it desires and an overall dia that it prefers, which can only be a difference of .0005". Now we are talking serious accuracy here, not minute of animal, but the theory holds true.
try this, jamm seat a barnes (all copper) bullet in the lands by .020" and fire it with the same load that you were using with a cup and core bullet seated .020" into the lands. Now, read your strain guage results and compare them to one another. You will find that density does have an effect on pressure, and to a smaller degree, a jacket difference in density or dia will have an effect on a cup and core pill. The barnes suggestion is just a larger more dramatic change to illustrate the effect. This is also why Lapua built competition bullets in .308" and .309" dia. They suggested you try each one, to see which dia made the most accuracy. That is all related to both pressure/gas seal, and bore dia.
if these nuances didn't exist, every bullet of simlilar weight and bearing surface length, could be used with the same load data. But we know that doesn't fly (no pun intended) /ubbthreads/images/graemlins/grin.gif
Quote:
jacket thickness differences as well as different harmonics. The barrel vibrates in the shape of the infinty symbol. the best groups are acheived when the bullet exits the muzzle at the intersection, however, a bullet/load may exit the muzzle at a different point, but do it consistently at the same point, and will show accuracy as well.
Jacket thickness coupled with a different "dwell" time than the v-max.
my .002"
Jacket thickness has no "bearing"( /ubbthreads/images/graemlins/smile.gif )on this. Where does this crap come from??
The vibrations in a barrel ("IF" it has them) do not form an infinity pattern - they are random, and they vary with different barrels, and are so slow that they cannot complete a single cycle before the bullet leaves the muzzle.
The "resonant frequency" of a barrel is only a hundred or so whips per second - the "dwell time" in the barrel of a high speed bullet is 1.5 to 2 milliseconds. So a "Dwell cycle" takes 10 milliseconds, the bullet is gone in 1/5th of a single cycle - in other words - if the barrel "is" harmonically vibration, the bullet is gone before 1/5th of the first cycle has started...
... do the math yourself!
.
jacket thickness i.e.(overall dia) and or a difference in jacket density/material will affect pressure. This is a very provable fact since some benchrest barrels won't shoot a J4 jacketed bullet and others won't shoot anything but a J4 jacketed bullet. I have some barrels that will fling a berger bullet into patterns, and others that will bughole them. The gunsmith told me that is just the way of things. Some rifling lands are higher, some are shallower, even in barrels from the same maker. It depends on the barrel itself, and the barrel dictates the jacket it desires and an overall dia that it prefers, which can only be a difference of .0005". Now we are talking serious accuracy here, not minute of animal, but the theory holds true.
try this, jamm seat a barnes (all copper) bullet in the lands by .020" and fire it with the same load that you were using with a cup and core bullet seated .020" into the lands. Now, read your strain guage results and compare them to one another. You will find that density does have an effect on pressure, and to a smaller degree, a jacket difference in density or dia will have an effect on a cup and core pill. The barnes suggestion is just a larger more dramatic change to illustrate the effect. This is also why Lapua built competition bullets in .308" and .309" dia. They suggested you try each one, to see which dia made the most accuracy. That is all related to both pressure/gas seal, and bore dia.
if these nuances didn't exist, every bullet of simlilar weight and bearing surface length, could be used with the same load data. But we know that doesn't fly (no pun intended) /ubbthreads/images/graemlins/grin.gif
