Thread: Chronograph
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Old December 27, 2012, 03:02 PM   #24
Unclenick
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Join Date: March 4, 2005
Location: Ohio
Posts: 21,023
Be aware the .22 calibration is for match ammo, which has been shown to be within about 50 fps of claimed velocity in most rifles. But be aware that is the limit of the accuracy of the calibration. Other than cross-comparison with other chronographs to get a sort of average agreement, the only other way I know of to calibrate them is with Doppler radar equipment, which can follow a bullet to the target, giving range and velocity constantly all the way to the target to within a small fraction of a foot per second. No consumer version exists that I am aware of, but military labs have them.

RSI has mention on his site of a German military study of chronographs for their armorers using Doppler radar. It found the Oehler and the CED matched most closely to the Doppler readings. But unless you do very long range shooting, that last gnat's behind in accuracy probably won't matter as much as repeatability so that you can see changes in your loads when you change components and test conditions and whatnot.

Along with the tripod, get a laser bore sighter. Take the bolt out of your rifle and put the bore sighter in and set the gun up on sandbags so its sight picture stays on the target. When you set up the chronograph, hold your palm or a piece of white paper in the middle of the screen area and adjust the tripod until the dot is centered in both the front and back screen area. When you go back to the gun, double-check that it is still looking at the target. If not, re-do the setup process. But if so, you will be surprised how high the target and sight appear to be inside the chronograph screens, despite the fact you are sending the bullet through their center. You will then understand how so many people accidentally shoot their chronographs.

CAUTION: Be sure you remove the bore sighter before putting the bolt back in the gun. The reason is explained here. Be sure you scroll down through all the photos.

Be sure you set your chronograph out far enough. Funny results are almost always due to being too close. I always use 15 feet just because the SAAMI specs call for that range. 10 feet is normally fine for handguns, but you get a lot of reports of funny result (too fast, too slow, erratic, always the exact same number, shots from adjacent firing points triggering the screen with muzzle blast, etc.) that turn out do be due to close proximity of the chronograph to the muzzle. We had one member with a .338 Lapua Magnum who had to set his unit back 18 feet before he stopped getting glitchy readings.

As for batteries, the 9V lithium cells are the ones to have for a chronograph. They not only last longer than alkaline, they can put out more current in cold temperatures and a spare one left unopened in your range box can stay at near full capacity for a decade or more.
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Last edited by Unclenick; December 27, 2012 at 03:08 PM.
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