Chronograph need and cost

[AzShooter]

I shoot competition and the bullet has to meet a certain power factor. Just going by the reloading manual I didn't make the chrono a few times.

Using my Digital Pro I am assured that my ammo is doing what it's suppose to do. I keep track of my velocity, average,standard deviation and extreme spread.

All of this adds up to very accurate and consistent loads.

 

[ka9fax]

I have the CED M2 and really like it. I think i paid 200.00 for it. It will store 1000 shots or 500 strings. I can download everything when i get home. I really like the big read out and the fact that the CPU part (display) sits on my bench. It has a 2 year warranty and mine was over that. My speaker went out and i wanted the new firmware upgrade. I sent it in and in a few days i got a call and was told my speaker was fixed and firmware updated, no charge and they shipped it back free. Good service like this means a lot to me.

 

[Clark]

I shot holes through (3) ~$100 chronographs;
shooting chrony
shooting chrony
Pro chrono

Those (3) each lasted about 5 minutes.

I bought a 4th, another ~ $100 Pro Chrono and only shot rifles over it and it has lasted 10 years. 10 years later I find I can shoot handguns over it, but only after shooting the handgun and making sure it is on the paper.

I got a magnetospeed ~$400. I clamped it on a 10/22 and it is still there collecting dust. I think I forgot how to operate it.

A big problem for me is shooting at 2,500 feet altitude in the sage brush where I hunt, the sky is too black to trigger the chrono.

So I have to turn the chrono on it's side to get a shadow with a box.

 

[g.willikers]

If all you need is safe to shoot ammo, the load data from the component manufacturers' web sites and manual publishers will do nicely.
After all, that's all we had to go by up until twenty years or so ago.

But if more precise loading info is needed, a chronograph is a must.
My old Chrony has served me well without complications, even after being wounded a few times.
It can give some mighty funny readings at times, but that's caused by lighting anomalies.
A clear, but evenly overcast grey day works best.

 

[Unclenick]

I'm less sanguine about the cheap ones after my dad had a light 168 grain SMK 308 load read 2700 over his Chrony one day, and I had my Oehler set up on the next firing point and it said 2500 fps for the same load. The Oehler was much closer to the book velocity for that load. I blame the lighting conditions, but concluded that IPSC had it right to put a pair of CED units in a black box in tandem and use electrically-powered infra-red sky screens with them to ensure consistent light and to reshoot any significant disagreement the two units had. Oehler's middle check screen handles that chore. But even it only gives an error when the disagreement is over 50 fps. So I figure that's about what you can count on for precision at rifle velocities when everything is working properly.

Since then, though, I've had both the Oehler and CED set up together in series and gotten very tight agreement. My guess is most units, even the cheap ones, work fairly well with the right light. The trick is knowing the right light is what you have. There's no good way to calibrate one other than by comparison or with a Magnetospeed or other light condition immune unit. CED has a good list on their page about their M2 chronograph of other things that can cause errors, like ground reflections. I notice Bryan Litz sells the large saber version of the Magneetospeed device. He's tried about every chronograph made, so he must be comfortable that it works well. It might not be a bad way to calibrate an optical unit. The LabRadar unit might also work for this, but they claim it's not good for finding BC's, so it sounds like they don't trust their own unit's accuracy.

Any ballistic table will tell you how much velocity to expect to lose at whatever distance you have from your muzzle to the center point between your sky screens. For typical pointed rifle bullets and pistol bullets near Mach 1 it is often about 3/4 foot per second for each foot of travel on the way to the midpoint between chronograph screens. In that case, you may lose 10-12 ft/s on the way to a chronograph whose screen center is at SAAMI's 15 ft standard distance. For something slow, like a round nose 45 Auto, despite a low BC, the low velocity also means drag is low enough that it only loses about 1/4 of a foot per second per foot of travel on its way to the chronograph screen midpoint, so only 3 or 4 ft/s second with 15 ft. chronograph distance.

 

[Colorado Redneck]

Some gray beard here in TFL said "If you haven't shot your chrony, you will eventually." One of my guns was giving me fits keyholing. Working on a load to overcome that issue, and seemed like I had found it. Then one of the rounds keyholed and the trajectory was altered enough that there is now a .204 caliber keyhole right square in the middle of the screen. I replaced it with the F1. Works fine. They may not be exact but if they are reasonably close to accurate and consistent that is better than nothing. If I shoot this one, same deal---F1 works for me.

I bought the last one on Amazon. Saved me about $20, and shipped free to my doorstep. Exactly like the original, same box, same rods, everything is identical. Except there is not a hole in the screen on the new one. Yet.

 

[wpsdlrg]

Never bothered with buying one, though I have rented one a couple of times. Basically, I load for accuracy....and let velocity take care of itself.

 

[Unclenick]

Gravity accelerates downward. A velocity difference that only causes stringing of a tenth of an inch at 100 yards can cause stringing of almost 18 inches at 1000 yards. It does depend on the bullet and how close to Mach 1 it is at 1000 yards, but the point is, if you do long range shooting you want to be able to minimize your velocity standard deviation during load workup at short ranges, where the stringing due to velocity variation won't normally be distinguishable from hold error. At 1000 yards it is.

 

[Arch in Maylene]

Been using a Competition Electronics Chronograph Pro Pal since 2008. Since I started, I wondered how I'd been testing my loads without one. It measures velocity and displays it on an LCD. I shoot, write down the velocity on a note pad and shoot again. The Pro Pal was a bare bones system.

Set up a spread sheet with the bullet data, charge, COL, etc., manually entered velocities and it calculated mean velocity, Stdev, muzzle energy and free recoil. My hand loads have stdev < ±20 fps.

Bought a new Caldwell chronograph because it specs velocity measurements of less than ± 0.25%; my old unit was ± 1.0%. The new chrony is hard wired to my iPhone 6S with a mini RCA jack. Set up instructions were poor, but once I figured it out, it copied all the data - velocities, energy, mean, stdev, temp, pressure and GPS position - onto an email and sent it to my computer. Minor complaints - iPhone is hard to read in full sun & it eats battery life.

 

[Mozella]

The main difference is in the bells and whistles. Some have a remote screen, keep track of a string of shots, figure average and standard deviation, and such. If you just want to know velocity, the cheapest Crony will do fine.

With the Caldwell, you get both. The unit is cheap because is has no "brains", no recorder, and no screen. But, if you have a smart phone like almost everybody does, you already own the "brains" and the screen. Hook the chrono to your phone, use the free app, and you have the best of both worlds; cheap chrono AND all the bells and whistles. It records all your data for transferring later into an Excel spread sheet, for example. You can even Email your range results.

The unit uses a relatively new design with a very fast clock speed, so like most electronic devices these days, newer means cheaper AND better. The basic unit is often sold for around 70 bucks and the deluxe unit with tripod and light kit can often be found on sale for a hundred bucks. If you have a tripod (or can buy one at a yard sale) and you don't shoot indoors, buy the basic unit.

 

[FrankenMauser]

The clock speed of the Caldwell unit gives it the increased accuracy.
But if they aren't assembling and calibrating them with the same level of precision, it is of little use.
Having the sensors tilted more than a couple tenths of a degree or installed farther apart than the design specification can create larger errors than the +/-1% of some other optical chronographs.

If the distance between the sensors is off by just 0.050", the calculated velocity will be off by at least double the advertised error.
Assemble the unit with a combined divergent sensor angle of just 5 degrees and the error is over one inch, just below the sky screens. And the amount of error will differ, depending upon how far above the sensors you fire the projectile. If you shoot through the center of the window, where the divergence is just 1/2", the calculated velocity will be 2% to 4.2% lower than actual. (I don't have any good measurements of the Caldwell chronograph. Otherwise, I could give solid numbers for the error - rather than a range.)


My point:
Don't read a whole lot into the advertised accuracy, unless you actually trust the company to assemble and calibrate the machines well enough to back up their claims.
If you don't trust them to be ultra-precise with build quality and calibration, then you can't trust anything their product is telling you.

I've been working on the circuit and detection apparatus for an IR laser-based chronograph (80 MHz) for about 6 weeks. In the process, I have discovered that if you can't build it ultra-precisely, then you have to be able to calibrate ultra-precisely. The electronics have to be reliable, too, but the distance between the sensors is the absolute crutch of optical chronographs. Screw up that distance without means to adjust for it electronically, and the machine is no longer trustworthy.

 

[Pathfinder45]

This is a quote from post #7:

Without the chronograph you won't accurately know your drop at distances.

I rather doubt that you can accurately know your drop by calculations based on velocity and B.C. I think that the only way to know is to actually shoot at all those distances.

 

[Unclenick]

FrankenMauser caught it. The accuracy is not really 0.25% just because the clock period is 0.25% of the bullet transit time. That makes the resolution 0.25%, not the accuracy. Chrony makes the same implausible claim of accuracy equaling resolution. It does little for my confidence in their technical staff, but maybe it's just the sales people doing it.

My calipers have 0.5 thousandths resolution, but if I apply too much squeeze pressure to the measurement, the accuracy is minus a couple thousandths. It'll show that erroneous number to the nearest half a thousandth, but the flexing of the parts means the number is not accurate.

The flexing jaws are analogous to sensor spacing errors, bullet glint errors, ground reflection errors, light source errors, penumbra sensitivity or other sensor sensitivity differential. Errors may also be caused by powder particles false triggering the screens when you are just too close to the thing for the amount and kind of wasted powder you are flinging out in your muzzle blast.

Really, the best solution to the spacing problem is a long beam. It makes a spacing error a smaller percent of the total. Both the Oehler and the old CED Millennium allowed for 4 foot and other spacing options. This, I am convinced, has a lot to do with their accuracy reputations. The newer CED unit has a higher clock speed and only 2 foot spacing available, but seems to do well despite that limitation.

One factor in long spacing is that not only do sensor location errors become a smaller percent of the total, but you tend to line the shooter up with the screens better. This is not a big source of error, but below is how the same degrees of error look with different screen spacing and how much it affects velocity. You can see how, with 12" spacing, an impatient person might settle for a degree of misalignment in a hurried setup that the person with 4 foot spacing couldn't even get readings over.