How do shooting chronographs work

Because most. Taking a. Otherwise, shooting through two chronographs of different makes in tandem is a good double-check to show that both are working properly under the particular conditions in question.

Paul from AccurateShooter. The Magneto Speed works different than most chronographs, in that it watches for changes in the electromagnetic field instead of light like most chronographs.

I like the idea of that, because issues related to light cause most of problems for other chronographs. It takes two velocity readings on every shot, and automatically compares those numbers to ensure they agree. If they are significantly different, it will alert you that there was likely some kind of error.

Knowing that the Oehler is essentially double-checking every shot, I have complete confidence that the velocity it displays is very, very accurate. It is also longer than most chronographs, and the further the distance between the two sensors the more accurate the chronograph is able to be all other factors being equal. I essentially envisioned lining up several chronographs so each shot would pass over all of them and recording hundreds of measurements and then really analyze the results.

You could account for the decrease in velocity as the chronographs got further from the muzzle. I think it would be enlightening. I would certainly be interested to see how it compares. The Magnetospeed appears to use sensor technology like that of an electric guitar pickup: a coil of wire wrapped around a permanent magnet. When a conductor the bullet passes close by, since it is moving with respect to the magnetic field lines, those lines induce current flow in the conductor.

That current has its own opposing magnetic field associated with it, and the interaction of the induced current magnetic field with the permanent magnet field distorts the latter, exposing the wire coil to moving field lines. Those induce current in the coil, which is detected as a signal by the chronograph electronics.

There are several things to keep in mind about this approach. One is that a steel-jacketed surplus bullet, which is not only a conductor, but is also magnetizable, will distort the permanent magnet fields a lot more than a jacketed bullet does. A lead bullet, which is a poorer conductor than copper, will distort the fields less than a copper solid because lower levels of current are induced in its greater resistance. Variation in velocity will also affect the size of the signal.

Bullet diameter will also affect how much metal is in close proximity to the field. The Magnetospeed makers have developed different sensitivities and different trigger signal profiles to adjust adequately for these factors, but you do have to remember to select the right settings for your bullet to get good readings.

You also need to record the settings you used to get future comparisons using the same bullet. The Magnetospeed units mount on the front end of a rifle barrel. Just as a barrel tuner affects rifle point of impact and group size, having the unit hanging off a rifle muzzle can affect accuracy, cause stringing, etc. For this reason, you have to work up accuracy loads and test their velocity separately, whereas an optical chronograph lets you do both simultaneously.

The military has found that post-muzzle effects acceleration, extra yaw, etc. That dozen calibers is inside the first Magnetospeed sensor spacing on some guns and calibers. It depends on how far the first sensor is from the muzzle.

It also means you will change that portion if the unit is not positioned to keep the first sensors exactly the same number of inches from the muzzle each time you use it.

It means that if I owned one, I would want to check how results compared to an optical chronograph set up so the start and stop screen midpoint was at 15 feet from the muzzle. The SAAMI standard velocity measuring system is optical and has its midpoint 15 feet from the muzzle. Since that is what commercial ammunition makers use, and I think it is best for comparisons for that reason.

Note that the military often uses 78 feet from the muzzle and you need to allow for that for comparison purposes. CalZ I am breaking in some new rifles and know they will speed up as they break in. I do not understand why when verifying ballistic data they want to adjust the bullets stated BC instead of the MV…I guess this article should educate hunters not to trust they chronographed numbers with so much confidence.

Sorry, I am a Texan and long winded [ vaccinated with a phonograph needle ]…Q: Which to you chose to adjust when doing the actual field verification shooting…BC or MV? CRaTXn cratxn me. I do the same thing on my coyote rifle. You should true the muzzle velocity when the bullet is in supersonic flight i. Most people never shoot at something into the transonic or subsonic range of a rifle, so most can stop reading there.

One field-expedient approach to correcting this variable is to shoot to the supersonic limit of the trajectory, observe the bullet drop and use it to correct the MV input. When the bullet slows to transonic speed, the drag modeling can become an issue. This can be field-corrected trued in much the same way as the MV input.

For best results, care must be taken to choose the truing ranges in terms of the transonic zone. Remember, truing is a calibration exercise and, as such, must be done with extreme discretion. Be patient. I will use data that I recorded while working up a load with one of my personal rifles, a. I decided which three powder charges to start with, one at 79 grains, one at 80 grains and one at 81 grains.

Everything about these loads is the exact same, except for the powder charge. I make four cartridges using each powder charge and then head to the range. With a clean rifle I put the first shot of the first load through the chronograph, in this case the 79 grain load.

I record the information and wait for the barrel to cool completely. For my second shot, I shoot the first bullet from my second load, 80 grains, record the data and wait for the barrel to cool. My third shot is with the third load, 81 grains and record the data. I shoot in this order to see the difference in velocities, but mainly to use one shot from each group of cartridges to foul the barrel.

Firing all four shots in a row from the same load out of a clean barrel will give you slightly inconsistent data. Let the barrel cool completely and look at the information you've recorded so far. From this point I shoot the remaining three cartridges in each of the three loads. Start by finishing the load from the third cartridge fired.

Below is my recorded data numbered in the order the cartridges were shot. You do not need to shoot any of these loads on paper. Your chronograph will tell you everything you need to know.

You can learn how many shots it takes for your barrel to be sufficiently fouled enough to obtain its optimum accuracy. From a clean barrel this rifle needed three shots to start to perform its best. In my experience, most barrels need just two shots from clean to start performing optimally. You can calculate your average foot per second velocity. Just divide the sum of the individual velocities by the number of shots. You can find your feet per second per grain velocity, which you get from dividing your average velocity by your total powder weight in grains.

With this information you can estimate the approximate velocity change resulting from adding or subtracting a single grain of powder. Most experienced hand loaders know the importance of a chronograph to accuracy, but shooters using factory ammo can also benefit from knowing the velocity of their projectiles.

A good chronograph will measure your velocity to within a few feet per second fps , plenty accurate to take the guesswork out of your ballistic calculations.

Most chronographs consist of two sensors a short distance apart that you shoot a projectile through while the unit is activated. This design is time-tested and will give you the results you need once you learn how to set it up and use it correctly.

But since most barrel-mounted units are made for barrels 0.