Chronograph Performance Review

[BryanLitz]

The Applied Ballistics Laboratory recently performed a comprehensive review of chronograph performance. This review is published in the book "Modern Advancements in Long Range Shooting". You can read the full chapter on chronograph testing here:

http://appliedballisticsllc.com/Articles/ChronographChapter.pdf

Based on our testing of available chronographs, we've decided to become a dealer of the Magnetospeed: Magnetospeed V3 Ballistic Chronograph in Hard Case

Knowing your true Muzzle Velocity is very important to accurate load development and trajectory prediction. We're impressed with both the accuracy and ease of use of the MagnetoSpeed unit.

Here's one short excerpt from the above link:
"The MagnetoSpeed takes the prize for the modern advancement
in chronograph technology. The instrument isn't necessarily more
accurate than the older Oehler units, but the use of electromagnetic
sensors provides comparable accuracy and precision in a very
different package which is easier to use. The accuracy and precision
performance of the MagnetoSpeed combined with its ease of set-up
and use are good examples of modern technology being put to good
use in ballistics instrumentation. The MagnetoSpeed is gaining
popularity in many applications including military snipers who need
a small instrument they can deploy with and check velocities of
different lots of issued ammo without setting up large instruments.
The potential effect on barrel harmonics was a big concern of mine
initially, but it just hasn't been a real issue for the kinds of rifles and
testing I've done with it."

-Bryan

 

[bill123]

Bryan,
Great news and an awesome endorsement.

In Modern Advancements... you said that you did not think that the Magnetospeed affected harmonics. Any opinion as to how much more weight on the end of the barrel would begin to affect group size?

 

[BryanLitz]

It's hard to tell. My testing was specific to the accuracy of the chronograph, and didn't really focus on group sizes. Having said that, for the barrels I typically shoot for testing which are 24" or 26" 1.125" straights, the affect on POI and groups with the magnetospeed attached was not noticeable.
The attachment is relatively 'soft' as opposed to rigid, which I think prevents the full harmonic effect as an equal weight attached rigidly.
For lightweight sporter barrels I suspect you may see the greatest affect of attaching the unit.
-Bryan

 

[idaho elk hunter]

With great reviews like these made me go purchase one. It works 80% of the time. I am kinda disappointed. After emailing them they said sorry and basically said it was my problem! I can say it is so much better than my old PRO CHRONO.

 

[Pdvdh]

I run a triplicate light sensing chronograph set up with all skyscreens mounted on a single rigid aluminum skyscreen rail. My three chronographs consist of an Oehler 35P, Oehler 33, and a PACT PC2. The Oehler 33 and PACT PC2 are older models, no longer available.

I use a 6' primary/3' proof channel skyscreen spacing for the Oehler 35P, a 6' spacing for the Oehler 33 skyscreens, and 56" skyscreen spacing for the PACT PC2. All skyscreens are spaced from a common center location on my skyscreen rail, such that all chronographs should record virtually the same velocity for each bullet fired over the skyscreen rail.

This setup provides a direct comparison of the performance of each of these three chronographs for every bullet fired. Both Oehler chronographs use the current model Oehler skyscreens.

All three chronographs provide more or less comparable quality of data, with respect to precision. They all deviate slightly, yet consistently, with respect to accuracy. For example, My Oehler 33 reads ~7fps faster than the Oehler 35P, however it very consistently reads 6-8fps faster than the Oehler 35P. I believe this is simply due to the fact that the skyscreen spacings aren't perfect for the calibration of each chronograph. In other words, if the skyscreens are spaced a little too close together or a little too far apart, the accuracy of the measured velocities will be affected. This is a primary reason why greater skyscreen spacing will result in more accurate readings. There's no way to know the exact location over each skyscreen that the bullet's passing triggers the chronograph computer to start/stop. The slot over the skyscreens is 1/3" wide. Increasing the spacing of the skyscreens reduces this source of error. I concluded immediately that greater spacing between the skyscreens would provide better accuracy, which is why I built a skyscreen rail designed for 6' skyscreen spacings.

How do I deal with the differing accuracy? I simply set the spacing of my skyscreens as close as possible to exact separation distances the three chronographs are programmed for, and live with the results. I know of no method to conclude which one of the three is providing the more accurate absolute velocity. So I average the three recorded velocities and accept that average as my actual MV.

The notable and consistent difference between the two Oehler chronographs and the PACT chronograph, is that in fading/failing light, the PACT will record an errant velocity, or most commonly - fail to record any velocity at all. The Oehlers will continue to function in dimmer light. Not a big deal. When my PACT begins acting up in low light, I know it's time to call it a day. I think the Oehler skyscreens likely provide better sensing ability in low light conditions compared to the PACT skyscreens.

Based on my fairly extensive use of this chronograph seteup, and direct comparisons of hundreds of shots fired and recorded, I would stress these three conclusions:
1) if you want to improve the accuracy of any light sensing chronograph, increase the skyscreen spacing to the maximum distance you find manageable. This becomes a matter of compromise. The longer the skyscreen spacing, the more tedious it becomes to transport the skyscreen rail to your shooting location(s). My compromise was the 6' skyscreen spacing, in order to keep transportation of my skyscreen rail manageable. My skyscreens are always mounted on a very rigid aluminum rail. It doesn't fold up. The rail is always 6' 9" long wherever it's stored, transported, or set up and in use.
2) all light sensing chronographs will periodically record bad data, or fail to record any velocity (goose egg). I'm uniquely positioned to identify bad data from any of my three chronographs because every bullet fired is simultaneously recorded by each unit. When one of my units burps out an errant velocity, the other two readings are generally still comparable and consistent. It's easy to identify the "bad" velocity. In these instances I run with the average velocity obtained from the remaining two chronographs.
3) based on conclusion number 2), there simply is no straightforward means of determining and knowing if the velocity recorded from a chronograph setup that only provides a single recorded velocity for each bullet fired is accurate, or bogus. I couldn't say that any one of my three chronographs clearly more often records bad velocity data. All three are occasionally guilty. Even Ken Oehler admits that light sensing chronographs can and will, occasionally record errant velocity. This is the primary reason he designed his Model 35P with the Proof channel, and where the value of the Proof channel becomes apparent in use. The Proof channel provides a means of identifying flawed recorded velocities. So I actually obtain 4 recorded velocities for each bullet fired over my skyscreen rail. Two velocities from the Oehler 35P, one from the Oehler 33, and one from the PACT PC2.

For those serious about being able to confidently collect accurate velocity data, I have to recommend the Oehler 35P, or some other combination of chronographs that will provide a minimum of two recorded velocities for each bullet fired.

 

[bigngreen]

With great reviews like these made me go purchase one. It works 80% of the time. I am kinda disappointed. After emailing them they said sorry and basically said it was my problem! I can say it is so much better than my old PRO CHRONO.

I've only had one instance of my Magneto not catching a speed and acting intermittent, I found that I was not pushing the plug in enough, it snaps in at the very bottom, I have caught every round for probably better than 500 rounds now.

 

[bill123]

I've only had one instance of my Magneto not catching a speed and acting intermittent, I found that I was not pushing the plug in enough, it snaps in at the very bottom, I have caught every round for probably better than 500 rounds now.

Same with me. 1 error and it was cord related as well. I know they had some problems with cords early on. I fount that the retractable one has worked flawlessly. I had 1 issue with the early version toggle that changes the screens. They don't use it on v3. MS was really apologetic and fixed it very quickly. I had great customer service experience with the cord issue as well.

 

[Pdvdh]

I should have clarified that my prior post only dealt with light sensing chronographs. I have no first hand experience with non-light sensing chronographs.

 

[bruce_ventura]

Great article Bryan. Thank you for making it available online.

I use a CED M2 for work and a Prochrono digital at home. It's good to see how well the CED M2 faired in your tests. It looks like the sleeper among all of them in terms of value. As you suggested, the SD performance of the CED M2 could be improved by increasing the distance between the sensors, which is easy to do. I could increase it by 3X and then multiply the velocities by 3.

I can't wait to test the CED M2 against the Prochrono, which I find a little easier to use.

Too bad about the SuperChrony. I thought that one was pretty cool. I have an idea. Cut your SuperChrony in half and increase the sensor distance by 5X! Then you should get a pretty good SD. What else are going to do with it?

 

[tim_w]

Bryan,

Excellent work. Thank you very much for taking the time and releasing this info to us.

I have been running dual CEDM2 with IR screens (covered top of screens in bright light use and for consistency) to reduce the effect of lighting variations as much as possible as I use the unit in and outdoors. One of the first things I noticed and was not fond of was the same as you noted, the flimsy support setup especially for the size of the window/screen setup. Its obvious that this was their attempt on keeping weight and packing size for portable setup to a minimum. For most it maybe acceptable as can be seen it did fair quite well in that setup.

I made a boxed frame cage setup out of square thick wall aluminum tube that I checked to ensure straight and squareness. This holds everything rigid. I also mounted two bubble levels, one on each end to ensure level setup.

I did find that by replacing the single bifold thin walled tube with a fixed thicker rigid one gives almost if not the same results and makes transport much easier than my cage setup.

A noticable reduction in ES and SD especially/more so on which every unit was setup at the target were the result of these changes. I feel it supports your conclusions as to the reasons for the deviations in results you collected on this unit, secondly, to give others a possible idea of something they could try.

My guess is that my unit is about as close as I can get to your 12' Oehler setup without increasing the spacing to what you have. Which is my really the only major grip, as minor as it may seem, with the CED M2. It does not allow the using of anything but the standard 24" spacing of the senors. Given the results it may be nothing but I would like to know for myself. I guess it could be done and then using a formula to compute the correct vel etc but that is likley more work for little to no gain.

One last note is I always powered them off a inverter power supply or AC so power supply fluctuations were kept as low as possible.

All in all, with the simple addition of a fixed rigid piece of square aluminum rod to replace the bifold lightweight flimsy piece from the kit along with the mounting of two small level bubbles leaves you with a very precise setup without stepping up to a ballistics lab level equip and $$$.

In your testing have you ever done any research into the variations in velocity of the bullet at the point of exiting the muzzle, how far it may keep accelerating, what distance velocity actually begins to erode enough to be measurable? I know some radar testing has shown 6-8" for acceleration but not erosion. At the same time I wonder what numerous variables that could effect this i.e. gas volume and its velocity exiting behind and surrounding the bullet after it exits (which could vary based on powder used and volume barrel length. specs of the bullet itself etc.. Not to mention effects of things like muzzle breaks that divert significant portions of these gases etc. Wondered if you have any thoughts on this.

 

[idaho elk hunter]

The retractable cord has never worked! The solid cord I have put forward and backwards. It is the one that works MOST of the time. I just wish they offered the information of cord failures that you knowledgeable people have clued me in on. I wish they would offer me the cords, even if I had to pay for them. There service was less than adequate for me. It is a shame that I received more knowledge on this forum than from the Manufacturer!

Maybe they will chine in as a sponsor if they care?

 

[Pdvdh]

I don't own a MagnetoSpeed and never tied one on to any of my rifles. It's not uncommon for users do report affects on POI with a MagnetoSpeed strapped to the end of their barrels. I use lighter profile #3 and #4 contour barrels. Large contour for me would be #5. I would be amazed if I didn't experience both a POI shift and change if group size after strapping a MagnetoSpeed onto the end of my lighter profile barrels.

I understand the romance with those using heavier contour barrels. Surely the larger contour barrels would be less affected due to the change in barrel harmonics. The MagnetoSpeeds are reportedly so convenient and accurate that I'm still tempted for purposes of grabbing an occasional MV, even with the full expectation of a POI shift.

I hadn't read of many disappointments regarding failure to function, and wasn't aware of the cable connector problem. The cable connection would need to be fool proof to endure repetitive forces of recoil.

 

[bigngreen]

I don't own a MagnetoSpeed and never tied one on to any of my rifles. It's not uncommon for users do report affects on POI with a MagnetoSpeed strapped to the end of their barrels. I use lighter profile #3 and #4 contour barrels. Large contour for me would be #5. I would be amazed if I didn't experience both a POI shift and change if group size after strapping a MagnetoSpeed onto the end of my lighter profile barrels.

I understand the romance with those using heavier contour barrels. Surely the larger contour barrels would be less affected due to the change in barrel harmonics. The MagnetoSpeeds are reportedly so convenient and accurate that I'm still tempted for purposes of grabbing an occasional MV, even with the full expectation of a POI shift.

I hadn't read of many disappointments regarding failure to function, and wasn't aware of the cable connector problem. The cable connection would need to be fool proof to endure repetitive forces of recoil.

Of all my barrels I've had ONE show a noticeable POI change and that is my heavy varmint taper 308 which moved POI over an inch up at 100 yards, it's the last one I though I would see a POI change with but it's obvious, none of my lighter taper barrels move enough to even consider, kinda opposite of what I was expecting.

 

[bill123]

The retractable cord has never worked! The solid cord I have put forward and backwards. It is the one that works MOST of the time. I just wish they offered the information of cord failures that you knowledgeable people have clued me in on. I wish they would offer me the cords, even if I had to pay for them. There service was less than adequate for me. It is a shame that I received more knowledge on this forum than from the Manufacturer!

Maybe they will chine in as a sponsor if they care?

Some time ago, I called them about my cord issue and they sent me a new cord. Cords are available on their website under "spare parts".