I have a Superchrono and a CED M2. I started having awful problems getting readings with the M2, even using the IR screens, decided to try the Superchrono.
In 8 shots of careful testing my Superchrono measured an average of 109fps (+94 to +128) faster than my CED M2 at velocities around 3,060 on the CED M2. I have read nothing but good reviews on the Superchrono. I haven't verified the M2 my ballistic indulgences are on-and-off, but I have some gut feel that I shoot higher at distance than calculations based on the chrono predict. So the M2 may be wrond, but . . ..
One superchrono review mentioned instructions in a table (from Steinert) about proper vertical distance, dependent upon velocity, between the unit and the bullet path. That was in:
http://gunsmagazine.com/the-speed-read/
"Paying attention to the instructions is not my strong suite, but it pays in this instance. The instructions include a table that tells the user the best heights to mount the unit below the barrel/target line if shooting from distances of 25 to 400 yards for various velocities. In my case, the .308 should be in the vicinity of 2,700 fps. The table suggests mounting the unit 8 inches below the barrel/target line for that distance and velocity."
I see no such table anywhere. Instead I see only 2" to 51" with no mention of different velocities and different distances. And I cannot see any reason for such. However I do see, at:
http://www.australianhunting.net/AHN_Journal/Articles/SuperChrono.htm
"The next string of shots from the .308 recorded near on 200 FPS lower than previously measured...nothing had changed except the distance the bullet was passing over the sensors. I repeated the test with my .243 with the same results. If the bullet was fired 35cm's above the sensors then the measured velocity was much the same as I had expected and measured on previous occasions. If the bullet was fired 65cm above the sensors, velocity readings would be well down, as much as 200 FPS. I don't know if these results were just quirks of this particular unit or conditions on the day, but I've repeated them with the same results on a number of occasions in conditions ranging from sunny to raining....with exactly the same results. . . . In my experience 35cm over the top of the sensors produced readings and accuracy in line with what I know my loads are doing."
In spite of this, the second piece somehow concluded that the Superchrono was "a great bit of kit." But in his experience that vertical distance was critical - too far and the readings got slow. Of course my readings were faster - maybe I was too close?
I did not measure and cannot recall the vertical distance between the Superchrono and the bullet path in my test. I had the unit carefully aimed and on a tripod immediately next to the CED M2.
I have asked Steinert about this and will try to post any help I get from them.
So much for my input. Does anyone know if there anything to this vertical distance business, and if not, can you suggest anything short of the kind of reverse engineering calculation Bryan Litz suggests to sort out my situation? I have the Kestrel and Litz's books, but I'm not familiar with the program he refers to for calculation of MV from bullet drop at distance and BC.
Obviously real world empirical evidence is the most accurate calculator of anything, including MV, but it certainly seems the long way around.
