If you use a chronograph a lot for decades, you'll eventually hit a chronograph component or the chronograph itself (if there are any of those machines still in use where the main unit is in front of the shooter). Those who haven't done so probably haven't been using a chronograph long, chronograph fewer than a couple of thousand rounds annually, or are incredibly lucky.
Or we just pay attention to detail in the set up.
I've been using chronographs for over 30 years for both ,22 LR lot testing as well as load development and testing under different ambient temp conditions. The only impact I've ever had has been a bullet jacket fragment from a plated bullet that came apart in the barrel. All it did was damage the sticker on the front.
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Set up matters in a chronograph given how they work. They use a capacitor that charges in between the time the bullet passes the first screen and the second screen and it then determines the time of flight velocity based on the charge in the capacitor. That time is then used along with the distance between the sensors to determine velocity.
In turn if the distance the bullet travels across the sensors is not 100% consistent, the velocity readings will be erroneous and/or inconsistent.
When I set my chronograph up, I open the bolt, set the rifle on a front rest and bag, and sight the rifle on the target. I then - again ensuring it is unloaded and the bolt is open - sight back through the uprights on the chronograph along the rifle to align the chronograph and stand. I also ensure the chronograph is level. The final step is to sight the rifle at the target and ensure the V uprights are aligned ensuring the bullet will travel straight across the uprights.
I also set the chronograph 15 feet in front of the muzzle. It's far enough to ensure the gasses expelled from the muzzle don't trigger the sensors and that the muzzle blast doesn't move the chronograph or move it out of alignment from shot to shot.
Finally, I take care to avoid low angle light across the sensors as that will cause erroneous readings. I no longer use sky screens on cloudless days but rather use a sheet of coroplast to provide an even background for the sensors. The sheet is also large enough to protect it from rain, and reduces issues with shadows and low angle light.
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Set up for a pistol is similar, with the exception that you align it for a standing height so that the bullet travels straight across the sensors and confirm the Vs are aligned before you take the shot.
