I went shooting this afternoon with some folks, including Lawrence and Mike the Musicologist. Then we went to dinner. And at dinner, I came up with an idea. Even better, my idea has almost nothing to do with my previous post. (It does use some of the same technology.)
Those of my readers who are People of the Gun probably know what a ballistic chronograph is. For those who aren’t: briefly, a ballistic chronograph measures how fast a bullet is going. You place a stand that has two evenly spaced “screens” in front of your gun, and then fire a bullet through the screens. As the bullet passes through each screen, the screen detects the bullet’s passage. The screens are a known distance apart, so by measuring the time difference between the bullet’s passage between the screens, you can determine how fast the bullet is going. Typically, the screens are connected by a cable to a “head unit” that displays the velocity of the last shot, as well as keeping records for all shots in a session (including averages and standard deviations).
Ammunition catalogs will typically give you a muzzle velocity, but that assumes a certain barrel length, certain atmospheric conditions, and other factors. If you really want to know how fast a particular load from your gun is – or if you load your own ammunition, which wouldn’t be in a catalog – you want a ballistic chronograph. (Knowing velocities is also important in determining trajectories; for example, how much a bullet of a certain shape that starts out at a certain velocity will drop at 100 yards, 200 yards, 300 yards, and so on.)
That’s kind of a simplified introduction. Here’s my idea: why not put Bluetooth into the base that has the screens on it? And then, make your “head unit”, the part that displays the velocity and calculates averages, standard deviation, et al, an iPhone/Android app? You pair the screen base with your phone using the app; the phone has all the smarts and does all the calculations. You probably don’t need anything more complex in the base than the equivalent of a Bluetooth headset; just something to send the elapsed time over to the phone.
I see two good things about this: first, you’re saving some money on hardware because you don’t need a “head unit”, just the screens and an app. Second. when you want to upgrade the chronograph with “additional features”, all you really need to do is upgrade the phone app; the piece with the screens can be really dumb, since it just measures elapsed time between the bullet crossing the screens. All the real effort can be handled by the app that communicates with the screens.
Standard Bluetooth (like your wireless headset uses) has a range of about 30 feet, or 10 yards. My understanding is that most people put their chronograph screens somewhere around 5 yards from the muzzle, so that’s maybe 15 or 20 feet. We can figure that there won’t be any obstructions between the phone (which is probably sitting on the shooting bench) and the screen unit, so Bluetooth ought to work for this. If we’re really worried, we could make the link Bluetooth Class 1 instead of Class 2, which would give us about 100 yards of range between the screen unit and the phone, but I think that’s probably overkill.
The only possible drawback I can see is power: the screens are going to need their own power source, but you could easily put a fairly large rechargeable battery into the base of the unit. Enabling Bluetooth on the phone and using the app is going to suck up some battery power, but I’m thinking no more so than a Bluetooth headset. I’d be surprised if you couldn’t get at least two to three hours of chronographing with your iPhone before it needed recharging (depending on how much of a charge you started with). If your sessions at the range testing hand loads run all day, an external battery pack for your phone solves that problem.
A quick Google search turns up nothing like this idea, and I don’t see any reason why it can’t work. If you do, please post in comments. If you like this idea and have the skills to build it, you’re welcome to take the ball and run with it; I’d put up a Kickstarter for it, except I have no EE skills that would enable me to build this device, and I don’t know anyone who does have those skills.
, and there was something in it that I found striking and moving:
. But I’ll admit: I’m intrigued by the book, and will probably purchase it at Half-Price when it shows up there.