SuperChrono at 1000 meters

On June 8th, 2013, posted in: News, SuperChrono by 0 Comment

Here’s a reply to a question about velocity measurement at 1000m:

I placed the SuperChrono on a bipod as usual and aimed it at a dish on a radio mast beyond the range of my range finder. I can definetively say it’s no problem aiming within 6-7 MOA.

Back to the angle of the incoming bullet. My own long range caliber is 270 WSM and I put a 135 grs Match King with a V0 of 960 m/s into the ballistics software. At 1000m remaining velocity is 372 m/s, thus supersonic and detectable by the SuperChrono.

The bullet drops 2.84 m from 900 to 1000m. If you know this and the chrono is at 1000m, aim it about 3m above the 900m mark. If you’d rather aim above your firing postion, aim it 9 x 3 = 27m high. This should be your average tree, I guess.
I think this aiming accuracy is entirely possible for people used to pistol sights and having become accustomed to the SuperChrono. You just need a tripod with a ball head. People with reading glasses should put them on while sighting in. The SuperChrono measures velocities both ways and you can turn it around and point it back towards the firing position
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At low velocities the angle of the Mach cone appoaches 90 degrees and alignment errors become less significant.

If you aim 30 instead of 27 meters above the shooting position, the error corresponds to less than 1 m/s for actual speed of 372 m/s.
 
Aim 10 meters off and the error is 2 m/s, see below.
270 WSM 1000m
You can play around with the spreadsheet yourself.  Click here: SuperChrono Precision Calculator. It’s embedded on the page and you can download it from the Excel icon bottom right on the spreadsheet.
You can try inputting 50m off from the correct aiming point over your firing position. The error is still only 8 m/s. Let’s say you have the real thing, a .338 LM with a 300 gr Sierra with remaing velocity at 1000m of 538 m/s. Allow for a deviation from the incoming angle of the bullet equal to 2m at 1000m and input the numbers as shown.
 338LM 1000m
This translates to a reading just 1 m/s off, or 99,8% precision.
Concerning getting velocity readings at 1000m, what other means than a SuperChrono do you have? An optical chrono will only give you a correct reading if you shoot within the width of the photocells. 
 
This is usually 4cm and the optimum detection area is not more than 5-6cm high and located some 10cm above the sensors.
How can you repeatedly hit something this small every time at 1000m? What about undetected shots from the optical chrono? What readings are you supposed to trust?
Tre_deteksjonsområder_600
The SuperChrono has a detection area big enough for any situation and every single shot is detected as long as it’s supersonic.
 

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