Magnum,
You still had a break-wire chronograph that was working? Cool!
When folks say their unit works great, they usually actually mean it
appears to work great. To know if it actually works great, you need to cross-check the calibration. Putting a unit up in tandem with another, so you can see the same bullet read by both, is the only means readily available to most people. It is something you can maybe do when you spot another chronograph unit being used at the range. They should be of different makes, so you don't duplicate errors.
I have done that with my Oehler 35P with the screens at 4 foot spacing and my CED Millennium (M1; earlier unit) with 2 foot spacing and had very good agreement. Bryan Litz also reported very good agreement between the Oehler and the newer CED M2, as well. In my case, I'm talking less than 12 fps difference pretty consistently, shooting bullets that lost about 3 feet per second between unit screen centers. In many instances the difference has been as little as 4 fps, and I suspect how carefully I tighten the Oehler to its EMT pipe beam is the main variable. I've also done the tandem test with my father's early model Chrony, and got 200 fps difference. If you get a big difference, all you know is that one of the units isn't right.
One way to determine which unit it is, is to fire Match .22 rimfire over both from a rifle. .22 Match tends to be within 50 fps of its claimed velocity when fired from a rifle. That's partly because the huge expansion ratio makes chamber variations less significant. Also, the .22 LR is out of steam about 16 to 19 inches down the bore, but it slows only gradually for a number of inches after that. So, if your barrel is 18 inches to 24 inches or so, it will all be within that 50 fps tolerance and is about as close to an absolute reading as you will get with any degree of convenience.
There is, somewhere on line, a John Barsness article on optical chronographs that is worth reading. He recommends not getting one with less than 2 foot spacing. The CED has a 2 foot beam, but it is hinged in the middle. It all packs up into a canvas carrying case you can buy as an accessory. It's very compact.
I got my CED partly because RSI reported a German military test of chronographs using Doppler radar had found the CED most accurate and very close to the Oehler, which placed a close second. Nobody else's was mentioned. I did it partly to be able to use CED's accessory infra-red LED diffuser replacement, which forces uniform light conditions. That is how the ISPC judges assess power factor at the Nationals. They fire sample ammo over two CED's in tandem inside a tunnel that blocks natural light, powering them only with the IR screens. They make sure the two agree closely enough to validate a reading. The Oehler check screen does the same thing.
Regarding light conditions, read through
CED's page. Scroll about 3/5 of the way down and you'll find a list of factors that can screw up readings. It's a worthwhile read and addresses some of what you were talking about. Lots of people add to diffuser attenuation, but many don't realize ground reflection glint off a bullet can cause false triggering, too. So there are some ducks to line up.
I can't say I'm surprised to see a non-commercial Doppler unit coming out. Several years ago I was contacted by a board member who was a retired radar engineer who had built his own and was thinking of commercializing it. I still have a trace he sent me of a handgun round. Unlike the unit Brian linked to, this was a plot of velocity vs. time. It was more interesting to me than a numerical peak number because you can then see how much acceleration your bullet picks up from muzzle blast. Unfortunately, the fellow who had that unit was going through his wife having cancer and he was not, I think, possessed of the necessary time and energy to pursue it further then. I don't know what's happened with that since.
In the meanwhile, as with almost all electronic sensors types, radar modules have appeared and have become very economical, for those not up to radar design work. So it was only a matter of time before someone made a chronograph from one. I don't know what this unit will cost. Figure that someone will do it cheaper at some point.
There is also the Magnetospeed unit available now. Like the radar unit, it would avoid the problem of light condition sensitivity. I just don't know anyone who has one to get a comparison of its consistency and durability with. It has the drawback that, since it mounts to the gun barrel, you won't be able to shoot for velocity and do load tuning at the same time, as it would affect how the barrel "vibrates".
