Anyone have experience with downrange distance-from-muzzle chronongraph technology? Large, loud, bag of wind in the neighborhood with no credibility in ANY subject claims he puts his immediately in front of his target--out to 100 yards--for "true" downrange readings. I know nothing about chronographs.

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Originally posted by TWL:
Anyone have experience with downrange distance-from-muzzle chronongraph technology? Large, loud, bag of wind in the neighborhood with no credibility in ANY subject claims he puts his immediately in front of his target--out to 100 yards--for "true" downrange readings. I know nothing about chronographs.

I use an Oehler 35P so it would be cost prohibitive to buy 3, 100 yard cables but with some of the chronographs available it would be possible to set it up at 100 yds. or whatever distance would be entertaining for you. I have seen people do it with chrony's and other makes and read the results with a spotting scope. Makes for a long walk if you have to re-set but there is no reason it can't be done.

A chronograph can be set at whatever distance from the gun that one wishes. Practical limitations include the ability to reliably hit the screen sensing area (and NOT hit anything important on the chrono works), and the necessity to go to the chronograph to read and reset it.

This weekend I took some 100 yard readings with my Oehler from three different guns, just as a matter of curiosity. However, unless you are attempting to prove/disprove the published B.C. for some particular bullet, or suspect a published B.C. to be significantly in error, there isn't much occasion to chronograph anywhere other than as close to the muzzle as practical. I usually set the rig at about 10 feet (mid-screen distance) from the muzzle and then add a very small correction factor for true muzzle velocity.

What exactly is your small correction factor? I am interested, because I also set up about 10-12' off the muzzle, and I would love to know true muzzle velocity.

As an aside, I have a PACT professional and a Beta Master Chrony, and I could set either one down range, and not have to do anything but go get the readings after a string of shots (10 shots max per string). I have considered doing this to verify velocity and give better drop calculations. It is easier to shoot at 100, 200, and 300, though, and that will usually give the best indication of drop.

I always thought that you want to read muzzle velocities, which is maybe 12-15 feet from the muzzle. At 100 yards you would get a greatly diminished velocity. I hope I understood the question right. Marlin

The reason to put a chrony downrange is after you know muzzle velocity, you can then corroborate your calculated drop charts with a downrange velocity average. Or you can just shoot and measure drop, and back-figure the velocity and energy from there. Either way, it's about knowing what loads are doing downrange, since BC is really a much more dynamic number than we want to admit.

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Originally posted by Dubbie:
The reason to put a chrony downrange is after you know muzzle velocity, you can then corroborate your calculated drop charts with a downrange velocity average. Or you can just shoot and measure drop, and back-figure the velocity and energy from there. Either way, it's about knowing what loads are doing downrange, since BC is really a much more dynamic number than we want to admit.

The theory is sound but BC at 100yds doesn't really play into it. You could have as much variation in your loads vel. at only 100yds. I see no harm in doing it, except possibly to the chronograph, but you still need the muzzle vel. for determine downrange, past 100yds, drops & wind corrections w/o shooting.

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What exactly is your small correction factor? I am interested, because I also set up about 10-12' off the muzzle, and I would love to know true muzzle velocity.

Although it varies somewhat, most high-intensity centerfires with reasonably steamlined bullets will lose around 300 fps in a hundred yards, or an average of about 1 fps per foot. The actual loss is a little higher near the muzzle, but adding about 1 fps for each foot that the center of the screens is located from the muzzle is a reasonable approximation.

If I have the screens ten or twelve feet from the muzzle, I'll usually round up the instrumental velocity for record keeping purposes to the closest even 10 fps. For example, if a 180 grain .30-06 load averages an instrumental velocity of 2739 fps, I'll record it as 2750 muzzle velocity. In reality, the difference in muzzle velocity and instrumental velocity at 10 or 15 feet is deminimus.

But if you REALLY want to know, set your screens at 10 feet and fire five shots for a reliable average, then do the same thing at 20 feet. If the difference is about 10 fps then the ballpark has held my best swing.

I've done this before to check BC on bullets. The first thing you have to have is two chronos, and then you have to shoot several over them so you know how close they are calibrated together. Otherwise getting a muzzle reading from one and 100 yard reading from the other will be meaningless. I may not ahve been clear, but you need to set them up about 3 ft apart and take a reading from both to see how close they will read the same shot to start with. Then you can measure the same shot at the muzzle and 100 yards.