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**JohnKSa** · March 31, 2012, 05:08 AM

I wasn't disagreeing, I was trying to provide an explanation to go with the observations you provided.

There are two primary causes of barrel motion/vibration. One is the impulse of the "explosion" of firing. That will cause the barrel to vibrate in a very consistent manner in terms of the frequencies generated. It's sort of like the effect you get when you hit a piece of metal with a hammer. The amplitude (size) of the vibrations will depend on the magnitude of the explosion, but the frequencies/tones of the vibrations won't vary significantly (if at all) because you're seeing the impluse response of the barrel and that doesn't change from one shot to the next unless something breaks.

The second cause of barrel motion is the force exerted on the barrel by the bullet as it travels down the bore. Sort of like the way a garden hose moves when you turn the water on. That motion will not be as consistent as the vibrations generated by the impulse of firing because the bullet's path down the bore will be less consistent (especially in terms of velocity), particularly when changing from one load to another.

So if one observed the barrel motion/vibration during a number of shots, one would expect to see some aspects of barrel vibration/motion that don't really change from shot to shot, even when switching loads and some aspects of barrel vibration/motion that do seem to be affected by the particular load being used.

Pretty much what you described.

My final comments were addressing your observation that it would be difficult to get a barrel to shoot well if the vibration "patterns" didn't mesh well with bullet exit times. It is a difficult problem to solve analytically, but one can often solve it heuristically by altering the impulse response of the barrel by changing its dimensions. If you shorten it, you change the impulse response and that alters the vibration patterns. Admittedly it's not really possible to say with any certainty exactly what the change will be, but the hope is that the new length/impulse response works better in terms of matching bullet exit time with a "quiet" point in the muzzle's vibration cycle/pattern.

March 31, 2012, 05:08 AM	#13
JohnKSa Staff Join Date: February 12, 2001 Location: DFW Area Posts: 24,985	I wasn't disagreeing, I was trying to provide an explanation to go with the observations you provided. There are two primary causes of barrel motion/vibration. One is the impulse of the "explosion" of firing. That will cause the barrel to vibrate in a very consistent manner in terms of the frequencies generated. It's sort of like the effect you get when you hit a piece of metal with a hammer. The amplitude (size) of the vibrations will depend on the magnitude of the explosion, but the frequencies/tones of the vibrations won't vary significantly (if at all) because you're seeing the impluse response of the barrel and that doesn't change from one shot to the next unless something breaks. The second cause of barrel motion is the force exerted on the barrel by the bullet as it travels down the bore. Sort of like the way a garden hose moves when you turn the water on. That motion will not be as consistent as the vibrations generated by the impulse of firing because the bullet's path down the bore will be less consistent (especially in terms of velocity), particularly when changing from one load to another. So if one observed the barrel motion/vibration during a number of shots, one would expect to see some aspects of barrel vibration/motion that don't really change from shot to shot, even when switching loads and some aspects of barrel vibration/motion that do seem to be affected by the particular load being used. Pretty much what you described. My final comments were addressing your observation that it would be difficult to get a barrel to shoot well if the vibration "patterns" didn't mesh well with bullet exit times. It is a difficult problem to solve analytically, but one can often solve it heuristically by altering the impulse response of the barrel by changing its dimensions. If you shorten it, you change the impulse response and that alters the vibration patterns. Admittedly it's not really possible to say with any certainty exactly what the change will be, but the hope is that the new length/impulse response works better in terms of matching bullet exit time with a "quiet" point in the muzzle's vibration cycle/pattern. __________________ Do you know about the TEXAS State Rifle Association?