Setting up your Chronograph–Remember It’s a Tool, Not a Target
How to Avoid Shooting your Chrono: There is nothing more frustrating (or embarassing) than sending a live round into your expensive new Chronograph. When setting up a chrono, we always first remove the bolt and bore-sight to ensure that the path of the bullet is not too low. When bore-sighting visually, set up the rifle securely on the sandbags and look through the bore, breech to muzzle, lining up the barrel with your aim point on the target. Then (during an appropriate cease-fire), walk behind the chronograph. Looking straight back through the “V” formed by the sky-screens, you should be able to see light at the end of the barrel if the gun is positioned correctly.
Adjust the height, angle and horizontal position of the chronograph so the bullet will pass through the middle of the “V” below the sky-screens, no less than 5″ above the light sensors. We put tape 5″ up on the front sky-screen supports to make it easy to align the bore to the right height over the light sensors. Make sure the chrono housing is parallel to the path of the bullet. Don’t worry if the unit is not parallel to the ground surface. What you want is the bullet to pass over both front and rear sensors at the same height. Don’t try to set the chrono height in reference to the lens of your scope–as it sits 1″ to 2″ above your bore axis. To avoid muzzle blast interference, set your chronograph at least 10 feet from the end of the muzzle (or the distance recommended by the manufacturer).
IRON SIGHT Rifles: A common mistake, particularly with newbie AR15 shooters, is to use the iron sights when setting the height of the chronograph. All too often, people forget that AR sights are positioned roughly 2.4″ above the bore axis (at the top of the front sight blade). If you set your bullet pass-through point using your AR’s front sight, the bullet will actually be traveling 2.4″ lower as it goes through the chrono. That’s why we recommend bore-sighting and setting the bullet travel point about 5-8″ above the base of the sky-screen support shafts. (Or the vertical distance the chronograph maker otherwise recommends).
TARGET AIM POINT: When doing chrono work, we suggest you shoot at a single aiming point no more than 2″ in diameter (on your target paper). Use that aiming point when aligning your chrono with your rifle’s bore. If you use a 2″ bright orange dot, you should be able to see that through the bore at 100 yards. Using a single 2″ target reduces the chance of a screen hit as you shift points of aim. If you shoot at multiple target dots, place them in a vertical line, and bore sight on the lowest dot. Always set your chron height to set safe clearance for the LOWEST target dot, and then work upwards only.
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Tags: Chrono, Chronograph, safety, Tech Tip
When using a chronograph, I put a strip of masking tape across the far end of the skyscreens about 2/3 of the way up. This gives me a good aiming or boresighting reference that’s well away from the pricey bits. I learned that one the hard way.
EDITOR: That’s a good idea–you can even get bright green masking tape now at painters’ stores. Regarding the height–if you get too high above the light sensors, some of the cheaper units will start to give inconsistent readings because the light beam spreads out. You need to check for the “sweet spot” with each brand of chrono. Closer to the sensor will usually give a more reliable reading; but farther up will provide more security against hitting the “pricey bits” as German says. We’ve found on a Shooting Chrony Beta Master, best results are achieved with bullet travel no more than 9″ above the sensor.
I ruined my first chronograph setting it up to close (within 2 feet) of my muzzle while shooting my 300winmag and the blast caved in the front of the plastic unit and knocked the lenses out of alignment and broker the tabs the lenses are mounted in on my unit. Still deciding on what to replace it with.
I use a string with a large loop to go over the scope and mount then tie a not 10 feet from the muzzle. Run the string down the top of the barrel this keeps the unit a constant distance, and gives a level and height reference to the bore.
My ChronoPal has had some adjustments made to the rear portion of the case by a 40SW. Lined all the parts back up, glued ‘em in, and she works great. Calibrated to an Oehler It works just as it did before; more character too!
John708 called me from th ranst week and told me his rifle was shooting very well but he was not getting the velocity he was expecting. I told him to come by on his way home and we would set up my chronogograph and chaeck his velocities. We set up my CED and his CED bcak to back and made a couple test shots. His CED was about 50 slower that what we knew the loads were shooting. My CED was about 100 FPS slower than what was expected. We set up my old inexpensive Crony. It was reading the velocities that we were expeciting. I gave my Oehler 33 away when I was told the CED with both white light and infra red screens would serve me just as good. Now I just don’t know and wonder if the CED can be adjusted/calibrated.
John708 said he was going to reserect his old Chrony also. We were very disapointed.
Nat Lambeth
If shooting over a chrono’ from the prone position off a bi-pod or similar, beware too of the muzzle sinking as recoil causes the front of the rifle to drop. I ‘killed’ my first chronograph shooting off a gravel covered firing point where I’d not given enough clearance to start with and an inch or two drop in the muzzle caused a bullet to clip the housing.
A very easy and simple tool to help you set up the chrony is a simple piece of string! Set your gun on the rest and sight your target (unloaded of course). Tie one end of the string to the rear scope ring or mount, then pull the string along the barrel to simulate the bullet path. It an easy visual thing to then know how centered left/right and up/down and angle the chrony needs to be.
Just set your rifle on a sand bag sighted on the target at the end of the range with the bolt off. Then place a black electrical tape across one end of the defuser bar to the other end at the recomended height (Example at 5 inches above sensor). Next place a one inch red dot target on the midle/center of the electrical tape. Then look through the bore and see if the red dot target on the tape is visible. If not make the proper adjustment to the chronograpgh position until its visible brough the bore. hope it works for you.
Thanks for all the great info people. I got my first chrono for Christmas and with this info it should help me not to blow it up.