Update: As of 2/4/15, I have received a review sample of the new v3 MagnetoSpeed chronograph. The present review covers the v1 only.
A while back, when I was updating the Chronographs article, I stumbled upon the existence of the MagnetoSpeed magnetic chronograph. Conventional chronographs involve shooting bullets between optical sensors, kind of like goal posts. The danger there is that inevitably, just about anyone who doesn't clamp their gun to a bench will eventually manage to shoot and destroy their expensive chronograph. While there are a variety of different designs, and some of them are cheaper to repair than others, the risk is still there.
In my previous chronograph article, I reviewed all the differences between the various systems in the market, all of which use the same basic tech.
Technically, all chronographs compute the speed of the projectile by measuring the time it takes to go from one known measurement point to the other. Most chronographs (CED M2, Oehler, etc) do this with arms and optical sensors which try to "see" the bullet flying over them. The main concern with this is that you are placing your chronograph downrange, and shooting between the two legs of the chronograph. This is about a 1' wide area, and if you manage to shoot your chronograph it's costly, annoying, and time-consuming to replace the broken parts.
If you don't consider yourself a paragon of accuracy with an immunity from flinch reflexes, you'll be interested in what the Magnetospeed does to alleviate the problem.
Within the Magnetospeed package, you'll find a "bayonet" style sensor attachment to clamp onto your barrel, a micro-SD card to store your results on, and an electronic unit which calculates velocities and writes the data to the included micro-SD card. There are also two kinds of cable lines, one traditional line and one auto-retracting one which extends, then locks in the length you want. The retracting one is a great idea in theory but the weight in the middle pulled on things and was annoying. So I found that the standard wire worked the best for my application.
About the Sensor
The sensor itself is a hook-shaped proboscis which you mount to your barrel, cinch it down with a strap, clamps it down like a pipe wrench, and then shoot. The nice thing about this is that the chronograph never risks being downrange. Even at a no-interruptions indoors range without cease fires, you'll be able to deploy and use the Magnetospeed chronograph safely. Within the sensor are a pair of magnets, which are used to detect when metal objects pass over them. An additional use for the Magnetospeed's bayonet is that it, well, contains magnets. You can use them to check to see for steel cored ammo, pick up small fallen parts, etc.
The sensor is capable of mounting to a variety of cylindrical barrel or muzzle device shapes, and worked well with all of the 5.56mm's I tried it with. My next experiment after this will be to try it with other calibers, starting at 7.62x39mm and working my way up to Beowulf. Keep in mind that you're really not going to be able to chronograph pistol loads out of this, due to the design of the sensor. Most pistol barrels shake or recoil as they're fired, which would generally remove the chronograph from the gun with each shot. There are apparently some revolvers with long enough barrels to fit it, but I've confirmed that it won't fit my Smith+Wesson TRR8, which has a 5" barrel.
There's also a new version of the Magnetospeed sensor bayonet out there, which supports a larger blast protection zone. The blast protection zone is a sickle-shaped curve to the sensor's body, which keeps the sensors away from the worst of your muzzle blast. The sickle curves back in so that the flat part, which contains the two sensors, is still in line with the barrel and the bullets travel just a little bit above the sensors. Using this on something really big may not be advisable; I'd check for testimonials before trying to mount it on a 50cal.
The Magnetospeed is supposed to be usable with suppressors as well; large outer diameters on the muzzle devices don't appear to be a big problem.
The Processing Unit
The sensor connects to the front of your rifle's barrel, and then there's a 3.5mm (or perhaps 2.5mm) jack which goes from the bayonet sensor to the processing unit. The head unit is a nifty bit of electronics with an LCD display and a set of lights. There are no touch screens, just a traditional large-pixel LCD display and simple up/down/enter navigation menus. Despite its lack of glitz, it works very well and can be configured for sensitivity. In addition to providing data display during operation, the processor also writes archived shot strings to standard CSV file on its microSD card, which you can then remove from the processor and download onto a computer. The only gripe I had about this was that it doesn't store timing between shots, so it's harder to spot where one string stops and another one begins if you don't remember to tell the unit that you've started a new string.
Even if you don't check the CSV file, the head unit's display does a nice job of displaying your results. I've tested 5.56mm IMR 4198 loads out of my 18" barrel, and I intend to have some fun with trying different barrel lengths to see what the speed differences are. To date, my results to date have been rather consistent across the several 10-round strings I've fired. Although I do lawfully own large-capacity magazines in California, I tend to only load 10 rounds because I prefer not to lose track of which hole is newly added to the paper.
When the Magnetospeed pulls a reading, its display area flashes (thanks to a built-in LED). This is enough to let you know out of your peripheral vision that it's successfully measured the shot, without being more obtrusive than the flash coming out of your barrel. The head unit doesn't come with a stand, but there's an L bracket on it with a hole which would probably allow it to be secured to a stand or post.
Depending on the sensitivity you set, it can work with cast bullets; you don't have to shoot jacketed, plated, or solid copper.
Examining The Results
As a professional Linux guy, one of the neatest things to me about this system is the fact that the output is completely standard. I've attached a sample of the output; it's an ASCII text file in CSV format, which you can load into any spreadsheet you want, from Excel to OpenOffice. The package also includes an SD card adapter, which lets you use this on any regular SD card reader. Given that this is stored in plain text, I'm confident that the provided 2GB microsd card won't run out of disk space, even if you store all your data forever on it.
Impressions of Use
As a battery-saving measure, I learned that the head unit won't power on at all unless the sensor cable is plugged in. This concerned me greatly when I first got it, because I thought it was possibly dead. But this wasn't the case, and the bayonet doesn't have to be attached, only the cable/plug. The good news is that because it has no power without the plug installed, there's no way you'll leave it on and kill your battery if you remember to unplug the cable before storing it.
I do most of my reviewing and shooting at IronSights, which is an indoors facility open until 10pm. They have a very nice setup, but they have somewhat small shooting booths. The booth counters are basically just support platforms, not "benches". So, given these space constraints it was a little clumsy to install the chronograph while handling the rifle. This made me glad that I was taking readings on rifles with bipods mounted. That having been said, it did run just fine once I figured out the right way to maneuver in the space I had.
By default, the processor will compute and display standard deviation, but it can be set to do extreme spread instead. It maintains a counter of shots, and tracks the FPS for each shot. The extreme spread vs standard deviation point is moot for CSV users, as you'll just compute whichever of those you care about in your spreadsheet yourself.
Note to self: Write something to parse the logs from the magnetospeed and present it with a happy, friendly graph via RRDtool, as a Gunwiki app.
The power source is a pair of AA batteries if I remember. It retains settings while turned off, probably via NVRAM storage.
I haven't used all the chronographs on the market, but I think for any/all rifle related shooting this is my chronograph of choice. At $250 it's right in line with the more expensive established chronographs, but my personal opinion is that the benefits of not placing your chronograph in harm's way or risking forgetting it, and being able to download the results to an SD card, all greatly outweigh any kind of further benefit which one of the more traditional and expensive chronographs may provide to an average shooter.
For the guy trying to test out his loads, it's perfect. For the guy who, like me, has less confidence in not lobotomizing his chronograph, it's perfect.
But even if you DID manage somehow to shoot your chronograph bayonet, the sensor module is in fact replaceable (although they're most of the cost of the unit).
Sample CSV Output
This is a sample of the output from my IMR 4198 load, out of a 18" barrel. I was shooting mixed brass, so there was little uniformity on internal case volume, which probably explains most of the speed variation.
[snewton@ares disk]$ cat LOG.CSV
Series, 1, Shots:, 5
Avg,2940 ,S-D, 174
ES , 346
1, 1, 3142, ft/sec
1, 2, 3119, ft/sec
1, 3, 2829, ft/sec
1, 4, 2815, ft/sec
1, 5, 2796, ft/sec
Series, 2, Shots:,10
Avg,2703 ,S-D, 53
ES , 173
2, 1, 2818, ft/sec
2, 2, 2747, ft/sec
2, 3, 2645, ft/sec
2, 4, 2685, ft/sec
2, 5, 2665, ft/sec
2, 6, 2698, ft/sec
2, 7, 2660, ft/sec
2, 8, 2705, ft/sec
2, 9, 2747, ft/sec
2,10, 2665, ft/sec
Series, 3, Shots:,10
Avg,2702 ,S-D, 38
ES , 132
3, 1, 2736, ft/sec
3, 2, 2698, ft/sec
3, 3, 2747, ft/sec
3, 4, 2615, ft/sec
3, 5, 2683, ft/sec
3, 6, 2702, ft/sec
3, 7, 2686, ft/sec
3, 8, 2724, ft/sec
3, 9, 2701, ft/sec
3,10, 2736, ft/sec
-- SeanNewton - 15 Feb 2013