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I own a Caldwell. It is one of the most unreliable gadgets I have ever owned. One of these days I will buy a real chrono.
Chronographs
- Thread starter KevinS
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You can not go wrong with an Oehler 35P chronograph. I have had one since 1987 and it works fine.
- Joined
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I am adding my setup procedure for the Oehler 35P.
I finally got my range pictures from my friend. I see two problems with chronograph usage that can affect the results.
The first problem is measuring from muzzle to start screen, and the other is not shooting straight through the sky screens. The velocity shown by chronograph is an instrumental velocity and not a muzzle velocity. The instrumental velocity must be converted through a ballistic program to make it a muzzle velocity. If you do not shoot straight through the sky screens, you will be going through at an angle which increases the sky screen distance for the projectile.
The chronograph uses two pieces of information for calculating the velocity. The first is using the program switches, which the user can tell the chronograph what screen spacing is used. The second is using the oscillator and the start/stop sky screens to measure the TOF (Time of Flight). If the projectile goes through at an angle, this distance will be increased. In this case I have the switches set at four feet spacing. But going through at an angle, could increase this distance to 52 inches. This will affect the velocity calculation and of course the displayed & printed velocities.
The first picture shows the shooter obtaining a shooting position. A target has been put up at 25 yards and the shooter is aligning the unloaded rifle with the target.
The second picture shows the rifle on the front bag. The shooter aligns the rifle with a point on the bag. In this case, the shooter uses the wedge with the back edge of the bag. This keeps the rifle at one firing position and maintains the muzzle to start screen distance. A small chain is attached to the forward screw. A string in this case, 14 feet long with a small hook, is attached to chain at a muzzle distance. Find a link closest to the distance of the muzzle. Before taking the rifle off the bag, measure from the center of bore to bench top. This measurement will be used later.
The third picture shows an alignment tool for the sky screens. The top sight is a red dot sight. The lower sight is a laser bore sight. These two sights are aligned at 25 yards. The top sight is placed in center of target and the laser beam will be aligned with that point.
The fourth picture shows the rifle and bag removed from rest and the alignment tool added to rest. It is important that the front rest NOT be moved after the shooter aligns the rifle with the target. The red dot is put on center of target and this will align the laser on that point. A measurement should be taken from laser to bench to be used later.
The fifth picture shows shooter pulling the string attached to chain toward the sky screen rail.
The sixth picture shows the string being attached to the start screen. Now the sky screen rail is positioned at 14 feet from muzzle. I have found that 14 feet is needed for muzzle loaders to get good readings from the sky screens because of debris from the barrel.
The seventh picture shows a cardboard target for aligning the sky screens with the laser beam. Notice the vertical center line and the mark showing the center of screen. Also there are marks at one inch spacing both above and below the center.
The eighth picture shows the alignment of the start screen with laser beam. Please be careful of laser beam and not look at it. The measurement taken from rifle to bench can be compared to the measurement from laser to bench. In this case, the bore will be one inch higher than laser beam. Please notice the green laser dot on the center line and one inch low. This will cause the projectile to pass through the center of screen.
The ninth picture shows the alignment of the stop screen with laser beam. Please notice the green laser dot on the center line and one inch low. The projectile will pass through the center of screen. Having the sky screens centered and one inch low, the sky screens are aligned with the path of the projectile for the most accurate readings.
The tenth picture shows the chronograph under the bench on the shooter’s box. This recommendation came from the factory. When a rifle fires, a shock wave will be produced. The bench will protect the chronograph from the shock waves and produce better results. Also it is better to stay away from other shooters, especially the ones with big calibers, while using the chronograph.
I have used this procedure with very good results. This procedure takes a while to setup, but the accurate results are worth it in the long run.
I finally got my range pictures from my friend. I see two problems with chronograph usage that can affect the results.
The first problem is measuring from muzzle to start screen, and the other is not shooting straight through the sky screens. The velocity shown by chronograph is an instrumental velocity and not a muzzle velocity. The instrumental velocity must be converted through a ballistic program to make it a muzzle velocity. If you do not shoot straight through the sky screens, you will be going through at an angle which increases the sky screen distance for the projectile.
The chronograph uses two pieces of information for calculating the velocity. The first is using the program switches, which the user can tell the chronograph what screen spacing is used. The second is using the oscillator and the start/stop sky screens to measure the TOF (Time of Flight). If the projectile goes through at an angle, this distance will be increased. In this case I have the switches set at four feet spacing. But going through at an angle, could increase this distance to 52 inches. This will affect the velocity calculation and of course the displayed & printed velocities.
The first picture shows the shooter obtaining a shooting position. A target has been put up at 25 yards and the shooter is aligning the unloaded rifle with the target.
The second picture shows the rifle on the front bag. The shooter aligns the rifle with a point on the bag. In this case, the shooter uses the wedge with the back edge of the bag. This keeps the rifle at one firing position and maintains the muzzle to start screen distance. A small chain is attached to the forward screw. A string in this case, 14 feet long with a small hook, is attached to chain at a muzzle distance. Find a link closest to the distance of the muzzle. Before taking the rifle off the bag, measure from the center of bore to bench top. This measurement will be used later.
The third picture shows an alignment tool for the sky screens. The top sight is a red dot sight. The lower sight is a laser bore sight. These two sights are aligned at 25 yards. The top sight is placed in center of target and the laser beam will be aligned with that point.
The fourth picture shows the rifle and bag removed from rest and the alignment tool added to rest. It is important that the front rest NOT be moved after the shooter aligns the rifle with the target. The red dot is put on center of target and this will align the laser on that point. A measurement should be taken from laser to bench to be used later.
The fifth picture shows shooter pulling the string attached to chain toward the sky screen rail.
The sixth picture shows the string being attached to the start screen. Now the sky screen rail is positioned at 14 feet from muzzle. I have found that 14 feet is needed for muzzle loaders to get good readings from the sky screens because of debris from the barrel.
The seventh picture shows a cardboard target for aligning the sky screens with the laser beam. Notice the vertical center line and the mark showing the center of screen. Also there are marks at one inch spacing both above and below the center.
The eighth picture shows the alignment of the start screen with laser beam. Please be careful of laser beam and not look at it. The measurement taken from rifle to bench can be compared to the measurement from laser to bench. In this case, the bore will be one inch higher than laser beam. Please notice the green laser dot on the center line and one inch low. This will cause the projectile to pass through the center of screen.
The ninth picture shows the alignment of the stop screen with laser beam. Please notice the green laser dot on the center line and one inch low. The projectile will pass through the center of screen. Having the sky screens centered and one inch low, the sky screens are aligned with the path of the projectile for the most accurate readings.
The tenth picture shows the chronograph under the bench on the shooter’s box. This recommendation came from the factory. When a rifle fires, a shock wave will be produced. The bench will protect the chronograph from the shock waves and produce better results. Also it is better to stay away from other shooters, especially the ones with big calibers, while using the chronograph.
I have used this procedure with very good results. This procedure takes a while to setup, but the accurate results are worth it in the long run.
