Precision Set-up Using the Vertical Sight Line
Precision Setup Using the Vertical Sight Line
The SuperChrono has to be aimed just as carefully as you’d aim your gun. Here’s a method for correct alignment that involves using the scope reticle in combination with the sight line on the back of the SuperChrono. The sight lines are the vertical black lines running down the front and rear of the chrono.
The method entails knowing the height of the sight picture from the bottom up to the center of the reticle. When this is known it’s uncomplicated to make the sensors parallel to the bullet path, see below.
The top image shows equal distance from the line through the sensors up to the bullet path. The lower image shows a setup that is not parallel, resulting in incorrect velocity readings.
Step 1. Find the height of the scope picture
First turn the scope down to its lowest magnification. Put the gun on a rest and aim at a yardsstick or measuring tape 3 meters or 10 feet from the muzzle. Keep the gun steady and make a note of the height from the bottom of your scope up to the center of the crosshairs. Repeat the procedure for 5m or 15 ft.
The table shows that a typical scope with 3x magnification and 42mm objective diameter has a distance from the bottom to the middle of the reticle of 7″ at 10ft. At 15ft the distance has increased to 11″.
Step 2. Place the SuperChrono the right distance from the muzzle
Mount the chronograph on a photography tripod with a ball head.
Position the chronograph 10ft (3m) in front of the muzzle. For magnum and high-speed loads place it 15ft (5m) in front.
Step 3. Position the SuperChrono directly below the bullet path
You will now position the chronograph directly below the bullet path. You’ll know you’ve got it right when the sight line on the chronograph is aligned with the vertical post of the reticle. Below at left is shown correct sight picture. In the rightmost image the SuperChrono has to be moved to the right to be directly below the bullet flight.
Seen from above it looks like this:
You will most probably spend a few minutes moving the tripod about until you get this right.
Step 4. Adjust the height of the chronograph
Center the reticle on the target and adjust the height of the tripod until the SuperChrono is visible in the sight picture as shown below.
Step 5. Aim the SuperChrono below the point of impact
Next and last step is to aim the SuperChrono. This is straightforward; use the sights and aim it at the target below the point of impact. How far below is determined by the distance from bottom of the sight picture to the center of the crosshairs.
Let us assume you have a scope with 3x magnification and 42mm front lens. The SuperChrono is 15ft from the muzzle. The table tells us that you should aim 11 inches below the point of impact on the target.
In practice you should aim at the imaginary red dot on the target:
Below are shown correctly and incorrectly aimed chronographs. Use proper sight picture for iron sights. Take a step back and look through the sights to make sure front and rear sights are aligned correctly.
The setup is now parallel as illustrated below:
It’s vital that you don’t adjust the shooting position, move the tripod or alter the height of the chronograph. If you do, you have to repeat steps 2 to 5.
Once you’ve got it all set up prepare for the next time around:
- Mark the spot on the ground where you’ve placed the tripod
- Mark how far the legs of the tripod are extended by using a (white) permanent marker pen or tape
Why it works
This method gives you readings within .5% of actual bullet speed. The reason is the perfect alignment:
- The SuperChrono has the correct sight picture with aligned front and rear sights aimed below the point of impact
- Every shot is fired at exactly the same height over and parallel to the axis through the SuperChrono’s sensors
High power scopes
Scopes with high magnification power have short distance from bottom of the sight picture up to center of the crosshairs. As it has no direct bearing on precision we have omitted to mention the fact that the bullet path normally is 1.5 inches below the sight line.
For high power scopes the bullet is precariously close to the chronograph with this method. A workaround is to place the chronograph at the top of the sight picture:
This doubles the distance you shoot over the sensors. You will consequently use the double of the distance in the table from Step 1. Let’s say you have a scope with 6x minimum magnification and 56mm front lens and have placed the SuperChrono at 15 feet. Look this up in the table and double the height.
In this case the height is 2 x 5 = 10″. In Step 5 you will aim the chronograph 10 inches below the point of impact.