Hi Bill
"CYA friends, after all these years since 1992, and what happened the other day with that RFBR gun, there's a little more light being shed on the subject of how a rimfire contraption vibrates, when fired, and how that vibration relates to rimfire accuracy."
This is something I looked into a while back and believe there is much more to learn.
Here is some results from some tests I did that may add to the knowledge pool to help with improving rimfire accuracy in the future.
This was measuring the vertical movement / vibration at the end of the barrel.
This was done by shinning an accurate laser measuring instrument at the barrel to measure distance.
This way there was no inertia or momentum with the measuring device.
The speed it measured was it took 40 readings from the time of ignition to the time the bullet left the barrel
From previous tests I had measured that at about 2.5 ms (milli seconds) which is 2500 us ( micro seconds ) depending on velocity
I need to explain what you are looking at.
This is a screen shot of an oscilloscope, the graduations down the left side is calibrated in MM so the smallest graduation is .01mm or .00039"
Along the bottom is the time and in this case it is in ms (milli seconds ) or 1/1000 th of a second
The ignition is at "0" and by the first graduation of "100" the bullet has well and truly left and gone as it left the barrel at 2.5 ms.
This is the overall big picture
Don't worry about the trace starting just under 0.06 mm on the left as this was the starting position of the instrument for this run.
This is another test with a zoomed in view, the scale on the left is still the same but the time is now in us ( micro seconds )
So the bullet left at about 2500 us or 2.5 milli seconds
Remember there are about 40 reading taken between "0" and "2500" when the bullet left.
Next thing is how accurate is the laser sensor ?
This screen shot is of the laser measuring a still barrel with nothing happening
This shows what we call noise or you could say the randomness of the measuring and it is a 1/3 of a division of .01mm so it is .003mm or .0001" (1/10 thou)
The specifications for the Laser measurement unit is within 1.5 metric microns or .0015mm or .000059" but I saw double that
The thing to note here is from ignition that the barrel starts to move down then back to the start height and then down again and back to the start height and stays there relatively flat for the critical time that the bullet leaves then starts to climb up which is the first upward swing on the "big picture" shot.
When I look back and forwards between several shots at the same settings you can easily see what is noise and what is a real movement.
Regards
Graham
"CYA friends, after all these years since 1992, and what happened the other day with that RFBR gun, there's a little more light being shed on the subject of how a rimfire contraption vibrates, when fired, and how that vibration relates to rimfire accuracy."
This is something I looked into a while back and believe there is much more to learn.
Here is some results from some tests I did that may add to the knowledge pool to help with improving rimfire accuracy in the future.
This was measuring the vertical movement / vibration at the end of the barrel.
This was done by shinning an accurate laser measuring instrument at the barrel to measure distance.
This way there was no inertia or momentum with the measuring device.
The speed it measured was it took 40 readings from the time of ignition to the time the bullet left the barrel
From previous tests I had measured that at about 2.5 ms (milli seconds) which is 2500 us ( micro seconds ) depending on velocity
I need to explain what you are looking at.
This is a screen shot of an oscilloscope, the graduations down the left side is calibrated in MM so the smallest graduation is .01mm or .00039"
Along the bottom is the time and in this case it is in ms (milli seconds ) or 1/1000 th of a second
The ignition is at "0" and by the first graduation of "100" the bullet has well and truly left and gone as it left the barrel at 2.5 ms.
This is the overall big picture
Don't worry about the trace starting just under 0.06 mm on the left as this was the starting position of the instrument for this run.
This is another test with a zoomed in view, the scale on the left is still the same but the time is now in us ( micro seconds )
So the bullet left at about 2500 us or 2.5 milli seconds
Remember there are about 40 reading taken between "0" and "2500" when the bullet left.
Next thing is how accurate is the laser sensor ?
This screen shot is of the laser measuring a still barrel with nothing happening
This shows what we call noise or you could say the randomness of the measuring and it is a 1/3 of a division of .01mm so it is .003mm or .0001" (1/10 thou)
The specifications for the Laser measurement unit is within 1.5 metric microns or .0015mm or .000059" but I saw double that
The thing to note here is from ignition that the barrel starts to move down then back to the start height and then down again and back to the start height and stays there relatively flat for the critical time that the bullet leaves then starts to climb up which is the first upward swing on the "big picture" shot.
When I look back and forwards between several shots at the same settings you can easily see what is noise and what is a real movement.
Regards
Graham