I picked up a used Lab Radar unit off the classifieds as an upgrade over my old Chrony (which still works well) with a goal of using it to study something that rarely gets discussed here - the variability of BC in the pellets as we shoot them, even though they are the same pellets out of the tin.
This is something that I have been curious about for years, ever since I first used average Chrony velocity data collected at two different distances (from two separate shot strings as I only have the one Chrony) and noticed that I was always getting a higher ES at distance vs at the muzzle – logic would say that since the pellets had lost a lot of speed, all else being equal the ES should be smaller. So all else is clearly not equal, and the big unknown to me was the BC on the different shots.
I am in the early stages of this, but even on my initial “proof of concept” trial I am seeing a lot of variation. I’ll have to do this again with more shots and better understanding of the humidity and barometric pressure, but I took 5 shots and got good trace data to use, so I did my test case on this data. It was shot from my .22 Huben K1, and was using JTS 18.1 grain pellets.
I took each individual shot file and truncated it for the S/N ratio data that I trusted – it was strange in that I was shooting at a steel spinner that was about 43 yards out, and it gave me velocity data for distances beyond that. But the S/N data clearly shows that this “extra” data is not good.
I then performed a quadratic polynomial regression analysis on each shot’s data, after having verified that the results proved to be an excellent fit. All five traces had R Squared values over .999, so the fit is excellent.
I then calculated the velocities for each shot at 0 and 50 yards from the equations and put each shot’s data in the JBM online BC calculator. While average of the five shots was a BC of 0.033 (approximate, as I was not precise on the atmospheric conditions – I’ll do better in the future), the five shots varied from a low of 0.030 to 0.035. While that might not sound like a lot, that represents a 15% swing in the BC of the individual shots. To me, that seems like a significant factor in long range accuracy . . .
More to come in the future as I continue to work on this . . . Here is what the data looks like.
This is something that I have been curious about for years, ever since I first used average Chrony velocity data collected at two different distances (from two separate shot strings as I only have the one Chrony) and noticed that I was always getting a higher ES at distance vs at the muzzle – logic would say that since the pellets had lost a lot of speed, all else being equal the ES should be smaller. So all else is clearly not equal, and the big unknown to me was the BC on the different shots.
I am in the early stages of this, but even on my initial “proof of concept” trial I am seeing a lot of variation. I’ll have to do this again with more shots and better understanding of the humidity and barometric pressure, but I took 5 shots and got good trace data to use, so I did my test case on this data. It was shot from my .22 Huben K1, and was using JTS 18.1 grain pellets.
I took each individual shot file and truncated it for the S/N ratio data that I trusted – it was strange in that I was shooting at a steel spinner that was about 43 yards out, and it gave me velocity data for distances beyond that. But the S/N data clearly shows that this “extra” data is not good.
I then performed a quadratic polynomial regression analysis on each shot’s data, after having verified that the results proved to be an excellent fit. All five traces had R Squared values over .999, so the fit is excellent.
I then calculated the velocities for each shot at 0 and 50 yards from the equations and put each shot’s data in the JBM online BC calculator. While average of the five shots was a BC of 0.033 (approximate, as I was not precise on the atmospheric conditions – I’ll do better in the future), the five shots varied from a low of 0.030 to 0.035. While that might not sound like a lot, that represents a 15% swing in the BC of the individual shots. To me, that seems like a significant factor in long range accuracy . . .
More to come in the future as I continue to work on this . . . Here is what the data looks like.
Distance | Shot 1 | Shot 2 | Shot 3 | Shot 4 | Shot 5 | |||
0 | 927.3 | 925.8 | 940.3 | 940.9 | 936.6 | |||
10 | 889.8 | 885.6 | 897.3 | 897.0 | 894.1 | |||
20 | 852.5 | 848.4 | 859.1 | 857.7 | 855.9 | |||
30 | 815.6 | 814.4 | 825.7 | 822.9 | 821.8 | |||
40 | 778.9 | 783.5 | 797.1 | 792.7 | 792.0 | |||
50 | 742.5 | 755.7 | 773.3 | 767.1 | 766.4 | |||
R Squared | 0.9997 | 0.9991 | 0.9995 | 0.9997 | 0.9997 | |||
G1 BC | 0.030 | 0.033 | 0.035 | 0.033 | 0.034 | ES = | 0.005 | |
ES (%) = | 15.4% | |||||||