On Tuesday, I tried my first ladder test. Actually I did the test twice with the same set-up.
Rifle: Savage M12 BR 6mm Norma BR / Weaver 36T scope
Bullets: Berger 105 gr BT Target
Powder: IMR 4064
Primers: CCI 450
I loaded 5 sets of 6 cartridges each. Charge weights were 27.7,27.9,28.1,28.3, and 28.5 grains.
I set the target up at 380 yards and used 3 sighters to get the POI where I wanted to start the test. I placed a digital video camera about 10 feet from the target and off to the side to record the shot sequence. I had also colored the bullets with Sharpies to differentiate loads, but in the end I used only the video to identify the shots.
For each test I fired 15 rounds in a "round robin" order, one round from each charge weight. Using a Shooting Chrony set up about 20 feet from the muzzle, I recorded the velocity of each shot.
When I retrieved the target after my first test, I was disappointed in the results. The pattern of the bullet holes looked more or less like a shotgun blast with some slight vertical elongation. I thought that maybe I did not have enough range in my velocities (charge weights) to obtain much useful data. The Chrony velocities were also not consistent.
Since I already had the rounds loaded and I couldn't practically move to a longer range, I decided to go ahead and redo the test with the same set-up.
The pattern of holes on the second target appeared more promising with a clear vertical stringing of shots with some overlapping shots near the middle of the string. Again the Chrony velocities didn't match very well with varying charge weights.
Back at the Bat Cave, I used the video to label each bullet hole in the sequence it was fired, 1-15, of each target. Then I measured the vertical distance from the point of aim to the impact for each shot. I entered this data along with the charge weights and the recorded velocities into an Excel spreadsheet for evaluation.
First I plotted velocity vs. point of impact (POI) and there seemed to be no relation at all. But when I plotted charge weight vs. POI, I was surprised to see that both tests provided similar plots, especially since the first test didn't look to mean anything at first glance.
Attached is screen shot of a graph of all the shots combined and pics of the two targets. Looks like around 28.2 grains is where I want to be for this combination. I can also see the Shooting Chrony has too much error for this kind of testing.
Rifle: Savage M12 BR 6mm Norma BR / Weaver 36T scope
Bullets: Berger 105 gr BT Target
Powder: IMR 4064
Primers: CCI 450
I loaded 5 sets of 6 cartridges each. Charge weights were 27.7,27.9,28.1,28.3, and 28.5 grains.
I set the target up at 380 yards and used 3 sighters to get the POI where I wanted to start the test. I placed a digital video camera about 10 feet from the target and off to the side to record the shot sequence. I had also colored the bullets with Sharpies to differentiate loads, but in the end I used only the video to identify the shots.
For each test I fired 15 rounds in a "round robin" order, one round from each charge weight. Using a Shooting Chrony set up about 20 feet from the muzzle, I recorded the velocity of each shot.
When I retrieved the target after my first test, I was disappointed in the results. The pattern of the bullet holes looked more or less like a shotgun blast with some slight vertical elongation. I thought that maybe I did not have enough range in my velocities (charge weights) to obtain much useful data. The Chrony velocities were also not consistent.
Since I already had the rounds loaded and I couldn't practically move to a longer range, I decided to go ahead and redo the test with the same set-up.
The pattern of holes on the second target appeared more promising with a clear vertical stringing of shots with some overlapping shots near the middle of the string. Again the Chrony velocities didn't match very well with varying charge weights.
Back at the Bat Cave, I used the video to label each bullet hole in the sequence it was fired, 1-15, of each target. Then I measured the vertical distance from the point of aim to the impact for each shot. I entered this data along with the charge weights and the recorded velocities into an Excel spreadsheet for evaluation.
First I plotted velocity vs. point of impact (POI) and there seemed to be no relation at all. But when I plotted charge weight vs. POI, I was surprised to see that both tests provided similar plots, especially since the first test didn't look to mean anything at first glance.
Attached is screen shot of a graph of all the shots combined and pics of the two targets. Looks like around 28.2 grains is where I want to be for this combination. I can also see the Shooting Chrony has too much error for this kind of testing.
