Two-Box Chrono

[Grungel]

Ehm.. Is this just not a copy of a device that existed for many years allready? What does it add, really? I am talking about SuperChrono.
http://www.steinertsensingsystems.com/product-details/superchrono-acoustic-shooting-chronograph/

Seems much more easy to set up. I just concider this as a nightmare to align.

 

[Grimstod]

Ehm.. Is this just not a copy of a device that existed for many years allready? What does it add, really? I am talking about SuperChrono.
http://www.steinertsensingsystems.com/product-details/superchrono-acoustic-shooting-chronograph/

Seems much more easy to set up. I just concider this as a nightmare to align.

I thought Brian Litz tested these and found they were really bad.

 

[adamjmac]

The SuperChrono is acoustic so there's no dependence on light condition, but that's about where the similarities stop. The value of the Two-Box is in having such a large sensor spacing. Increasing distance is a simple way to get a ton of more precision out of your timing measurements without significantly adding cost/complexity.

Also, it's a lot easier to align a 15 foot span than an 8 inch span. The sights are so far apart that getting them within 1-2 moa is a lot more practical. And this is what you need for accuracy of the average velocities that it reports.

To Alex, if you care about average velocity, you need to align them this well. But if you care about getting numbers that track along with the true variation in your shots, then you don't have to focus on alignment so much. Just put the boxes at the right distance and make them reasonably level and you'll get what you need for SD and load development. This is what I do and it literally takes 30 seconds and I'm ready to shoot.

If you want true velocity AND you shoot prone, then put one box flat on the ground and lift the other with something like a thin board, to get them lined up.

 

[TxGR]

Ehm.. Is this just not a copy of a device that existed for many years allready? What does it add, really? I am talking about SuperChrono.
http://www.steinertsensingsystems.com/product-details/superchrono-acoustic-shooting-chronograph/

Seems much more easy to set up. I just concider this as a nightmare to align.

Rex (

) did an initial review of the superchrono that looked promising, but he wanted to do more testing. I was seriously considering the superchrono until I read this review by Ryan Pahl (http://ryandpahl.com/?page_id=1810). In it, Ryan spells out several specific issues with the superchrono:
- the superchrono device needs to be somewhat elevated and away from objects that will reflect sound like the ground
- alignment is critical because tilt relative to the bullet trajectory causes huge errors, 1* changes the readout by 100fps (lack of accuracy)
- speeds are rounded to nearest meter per second, then converted to feet per second (lack of precision)

Ryan concludes sound is too slow to be useful. Measured at the short distance between the sensors on the superchrono, I suspect he is right.

At the longer distance between the two-box chrono sensors, I think most of the weaknesses in using sound are mitigated. The long measurement arm make alignment errors highly unlikely. Certainly, anything beyond ~1 moa would be glaringly obvious. I suspect, measuring over the longer distance also minimizes error because the distance from the bullet to the sensor is so much smaller than the distance between the two sensors -- but I am no sound guy.

 

[adamjmac]

Rex (

) did an initial review of the superchrono that looked promising, but he wanted to do more testing. I was seriously considering the superchrono until I read this review by Ryan Pahl (http://ryandpahl.com/?page_id=1810). In it, Ryan spells out several specific issues with the superchrono:
- the superchrono device needs to be somewhat elevated and away from objects that will reflect sound like the ground
- alignment is critical because tilt relative to the bullet trajectory causes huge errors, 1* changes the readout by 100fps (lack of accuracy)
- speeds are rounded to nearest meter per second, then converted to feet per second (lack of precision)

Ryan concludes sound is too slow to be useful. Measured at the short distance between the sensors on the superchrono, I suspect he is right.

At the longer distance between the two-box chrono sensors, I think most of the weaknesses in using sound are mitigated. The long measurement arm make alignment errors highly unlikely. Certainly, anything beyond ~1 moa would be glaringly obvious. I suspect, measuring over the longer distance also minimizes error because the distance from the bullet to the sensor is so much smaller than the distance between the two sensors -- but I am no sound guy.

All correct, except one detail. Distance from the bullet to the sensors actually doesn't matter at all. The shockwave cone has a shape that moves forward, so the sensors can be close or far, as long as the shock is loud enough the cone will hit the sensors will report correctly. The time *difference* between hitting the first and second sensor is what is measured, regardless of whether that's near or far from the bullet. As a result, it can be placed on the ground and you shoot way over top.

Also, reflections are not an issue because the first thing to hit the sensor is the shockwave itself. Any echos, muzzle blast, etc. are rejected because they happen later.

 

[jlow]

Adam, you should have a talk with Brian Litz. He was initially interested in using the LabRadar for truing BC but that had to be done down range and this cannot be done with a LabRadar due to triggering. If your 2-box can do this, he would likely be very interested in it.

 

[spclark]

If your 2-box can do this, he would likely be very interested in it.

I agree!

Even better: integrated 4-box system w/ remote data feed (not unlike what SMT target system does) for both firing line AND down-range ballistic data recording & analysis.

 

[TxGR]

--snip--
The value of the Two-Box is in having such a large sensor spacing. Increasing distance is a simple way to get a ton of more precision out of your timing measurements without significantly adding cost/complexity.
--snip--

I re-read through your website and instruction manual.

When I first looked at the raw data, I was taken aback by the speeds you were recording, and then I realized you were reporting mili-seconds, not fps. I was trying to understand how you tested accuracy and precision. Your instructions suggest setting the first box within 6 to 12 feet, but if I understand the test, you setup 10 two-box chronos in sequence. The test measured consistency from chrono to chrono (good demonstration of precision), but did you run any accuracy tests compared to other chronographs or mathematical calculations based on known factors.

I currently have an Oehler 35p, but I am interested in having a non-optical chrono too. The LabRadar gets wildly mixed reviews and doesn't work at all on short ranges. The superchrono is a non-starter (per earlier post). The MagnetoSpeed gets good reviews, but I don't like the poor repeatability (based on mounting) and the results of Litz's tests only shows moderate performance. Your chrono shows great promise.

You might reach out to Ryan Pahl (RyanDPahl.com) and offer to loan him a two-box chrono for testing and to do a review. He is also Canadian, but I don't know from what province. He did a video review of the superchrono and ran extensive tests revealing a serious precision flaw in that system. I don't know him and never heard of him before 10 days ago, but through his videos and research I can see he cares about accurate, repeatable tests and openly publishes raw data for review by others.

Thanks for developing this (and the autotrickler).

 

[adamjmac]

I am shipping three of them to Bryan Litz for testing. I believe he uses an 8 foot Oehler as a baseline so I suggested sending multiple because otherwise you won't know whether the error is coming from the Oehler or the TwoBox.

There's no way to 'test' accuracy because it is a user controllable parameter. However I do understand the geometry and I have a simulation I use to predict the velocity error given a geometry change. If the boxes are aimed 1 moa off in pitch, for 2800 fps bullet it will be off by 2 fps, so that's the baseline accuracy I can claim given a correct (and reasonable) setup expectation.

Thanks for the suggestion about Ryan Dahl, I'll reach out.

 

[micmac]

Any news ? Any reviews ?

 

[adamjmac]

I should say, it's a common misunderstanding that full extension of the cable is 15 feet. The 15 foot marker is the last mark on the cable and the cable is meant to have a few feet of slack.

 

[wolfman]

I'm glad you mentioned that- I would have totally missed it!

 

[steckmeyer]

My son and I took ours out last weekend. We shoot prone and wanted to see how it does along side our Labradar. I made the compulsory 15' error setting up so the velocities were 3-400 fps slower than the Labradar. We know the Labradar is correct so I did not do any further evaluation. Both the Two Box and the Labradar recorded all 50 shots fired. The Two Box seems to be of high quality construction and obeyed the little remote. The menu is straight forward and functional. The cloth bag is well thought out. I did not save the shot string so I did not have anything to evaluate on my computer. We will get it out again in a few weeks and be better prepared to set it up correctly.

Both of my sons and I are fully dependent on Adam's powder trickler. If we ever have to go back to hand dispensing powder we will all need serious therapy. I bought the Two Box because of our experience with Adam and the trickler. I suspect the Two Box will be in the same class and far superior to the optical devices.

 

[txsendero]

I made the same 15' error setting mine up the first time I used it last weekend, should have measured it to double check, but that's my fault. My readings on 7mm Rem Mag were also about 300-350 fps low because of the longer cable distance. However, I went ahead with my load work up and was able see where my velocity started flat lining at the top of the charge range. It picked up every shot, and this should be a lot better for load development since there's nothing attached to the barrel.

 

[adamjmac]

The video is live!

 

[1lnbrdg]

So, after watching the video, I don't shoot off a bipod for load testing, I shoot off a bench.

Will I have to have 2 tripods to get the boxes up off the ground or will they work fine sitting on the ground with me above them on the bench?

 

[adamjmac]

It will work fine shooting way over. You can leave them on the ground as long as you put them far enough in front that it's not too steep of an angle from the muzzle down to the first box. 45 degrees is a good rule of thumb if your bullet is over 2000 fps.

 

[DRNewcomb]

So, after watching the video, I don't shoot off a bipod for load testing, I shoot off a bench.

Will I have to have 2 tripods to get the boxes up off the ground or will they work fine sitting on the ground with me above them on the bench?

Just drawing some lines on a sheet of paper and thinking about it, 'seems to me that increasing the distance from the line of the bore would increase any errors caused by angular divergence. So, you might get different readings at a different range but it would probably not worsen the accuracy of a single session. (Did that make sense?)

 

[adamjmac]

If you are directly over top, shifting higher or lower doesn't increase the error due to pitch angle. The bore line has one pitch angle, and the chrono boxes have another. No matter if you move those lines closer or farther apart, the angle between them is always the same.

However, if you are not shooting directly over, to some extent you are shifted to the side, then all a sudden horizontal angle matters, whereas directly over top it doesn't as much. So shooting higher over top makes it easier to be directly above, and therefore less sensitive to shooting at left/right targets.

So even from a bench, it's better to leave them lower, but if you are too far over, then wind fluctuations can start to affect it. Try for 1-3 feet and you should never have a problem.

 

[jlow]

DRNewcomb is mirroring some of my own concerns. Some of the benches we shoot off is like 3 feet high – I realize that the numbers off a string will be consistent but I want my numbers consistent between outings. Also we frequently shoot off berms which slope away from the shooting position, sometimes into ditches, so that has to be taken into consideration.

Having used a Ohler 35P for many years, one big advantage of the LabRadar for me is never having to work in front of the muzzle point area and having to call time out. People don’t usually complain but I’ve always felt under the gun (literally and figuratively) trying to get the thing to work and hoping that I don’t end up shooting the thing. Obviously, I don't think shooting the 2-box chrono will be an issue unless we have to raise the boxes up but it does seem more work setting this up.

I know I am sounding like I am complaining but frankly just sharing some of my own experience and concerns.