With the skyscreens set up and the tripod properly adjusted to give your bullet the best path to travel, it was time to get things going with the MKIV-XP.
Plug the cable from the closest detector into the START jack and the furthest
detector into the STOP jack.
The MKIV-XP is enabled by pushing any of the keypad buttons. Once the unit has been powered up, pushing the CHRN keypad button will change from timer mode to chronograph mode as shown above. If you are using a detector spacing other than the default 18" value (as shown), you can change it by pressing the SET key, entering your separation (in inches), and then pressing SET again.
In the above photo, I already had accumulated thirteen previous strings of shots. The MKIV-XP is ready to record the first shot of the next string (#14) when the GO key is pressed.
With each shot fired, the chronograph beeps and displays the shot number and velocity (in FPS) on the top line of the LCD display. The bottom line displays the current average velocity. A variety of statistical data is available while reviewing the string of shots, including highest and lowest velocities, standard deviation, mean absolute deviation, extreme spread (difference between the high and low shot velocities), and the average velocity. You can EDIT out any individual bad shots by pressing the NO key during the review. Doing so will cause the statistical summaries to recalc.
You can continue adding shots to the same string by pressing the CST GO key on the keypad or a new string of shots can be created by pressing the GO key.
How does the MKIV-XP measure the bullets speed? Each skyscreen contains a photo transistor which is constantly monitoring the current light levels. The bullet is darker than the sky and so when it goes over the skyscreen, the light level drops a tiny bit. The MKIV-XP is sensitive enough to detect this slight change in light intensity and so the the clock is started (triggered by the START detector). When the bullet passes over the STOP detector, it is detected (again) and the clock is stopped. The velocity is calculated based on the time it took to travel over a known distance, which in my case was the 18" separating the two detectors.
Note that you should bring a few spare 9 volt batteries with you to the range. The manual states "skyscreens just eat batteries". When the detectors are plugged into the MKIV-XP, the detection circuit is active. When you are not chronographing, unplug the screens to conserve the battery.
Once you have gathered the data at the range (each string of shots is stored
in memory), you can plug it into your PC (using the non-supplied USB cable) and
download the shot string information.
The software is available from the PACT web site. The
download goes quick as the software is quite compact. Before initially
plugging the MKIV-XP into the USB port, install the software. From then
on, you only need to start the software before attaching the MKIV-XP to the PC.
Once the MKIV-XP is connected, the software will detect the USB port being used
and prompt you to press the OPTN key on the MKIV-XP. At that time, it will
ask if you wish to establish communications with the PC.
With the link established between the PC and the MKIV-XP, the PACT software displays a screen that allows you to choose what you wish to transfer to the PC. You can select Timer data, RPM data, Chronograph data, or all of it. In the above photo, chronograph data was selected and subsequently displayed.
You can save the data as a comma delimited file which can be easily imported into a spreadsheet, such as Microsoft Excel (which I use). Once in the spread sheet, I add a bit more info (gun & load) and then let the spreadsheet calculate the average velocity and standard deviation each string of shots. This is then incorporated into my reloading notes along with information about how accurate the load shot on target. I can then refer to my reloading notes at any time to determine how a load performed overall (velocity and accuracy).
I've found the chronograph features of the MKIV-XP to be very
helpful at the range. I no longer have to guess/estimate about the
velocity of the load. Comparing the real world performance numbers to
those from my reloading manuals makes the entire reloading process more
manageable, productive, and safer, in my opinion. I'm not looking to turn
this into a scientific study, but rather the great hobby I have always found it
to be....and now, a little bit better as I know just how fast (or slow) those
bullets are moving.
4x4 Off-Road Homestead Firearms RC Flying