Getting Your Inputs Squared Away Part: 4
Ok, you’ve got your text fields done and your barometric pressure measurement done. Now we need to do some of the inputs that have math done against them. These will affect your solutions so it’s important to be as precise and decisive as possible.
Let’s start with the yellow boxes: Metric Distances, Heading, Transonic Velocity, MOA:MRAD:Inch, Hectopascals. These are yellow because it’s encouraged that you leave them alone unless you know that you need to change them. They’re set with values that will give the broadest utility for most shooters.
Metric Distances: This is just to set the system to use metric distances for range. If you’re a metric system user you should actually leave the box alone and let the “Full Metric” option select it for you. In fact, it’s meant to be properly set up without any user input for those that use SAE ranges and for those that use metric ranges. For those rare sets of Americans that use metric ranges instead of yards but use SAE measurements for everything else will be the ones that want to put a “m” in the box. Putting an “m” in the box (lower case) will force the system to use meters for distances both large and small which are measured in linear distance. Angular distances will not be affected.
Heading: Leave this alone. It’s critically important for Coriolis calculations and it’s set by default at 90 to give you a full value. Your actual heading during firing will change but you actually use the cosine of your angle away from north or south as a multiplier for shots not facing directly east or west. In any event, you should leave this box alone.
Transonic Velocity: This is basically the point at which Ballistic_XLR will stop calculating. The reason for this is that when bullets go transonic they’re typically going to become unstable or at least less stable and any numbers that Ballistic_XLR provides after that are going to be wrong. If you know that your bullet is acting stable further then you can lower the number to as low as 1050. Note that doing so is unsupported and whatever results you get from that are considered spurious. Basically, leave it alone.
MOA:MRAD Inch Equivalence: Angular units of measure get translated to linear measurements in one of two ways. Either the distance is tracked as denoting the arc between to angularly separated points or traversing a straight line that transects both points. The first method describes a curve, the second method a straight line. Since curves are longer there is an opportunity for engineers to not make life easy. Some scopes use 1.09″:MOA@100yrds as the standard. Most use 1.05″:MOA@100yrds. At least one model of scope I’ve encountered used 1.01″:MOA@100yrds. This leads to some scopes always dialing in 4% more or less dope than they need. If you’re always coming in 4% high or 4% short in your initial adjustments, try changing this value to 1.09 or 1.01. Many Nightforce, Leupold and Sightron scopes have shown this feature. It’s best to do a scope calibration test at the bench to verify your click value. I’d do it at 300 yards too. We’re talking about .04″@100yrds. That’s 1.2″ at 300yrds and thus it is substantially easier to discern the difference at longer ranges.
Hectopascals/Millibars: If you are using this then you’re almost certainly using full metric. If you’re not using the full metric option then just leave this blank. If you are using the full metric option then filling this box in with your current Hpa value and adding a “Y” to the box immediately above it will convert your pressure to inHG and add it to the Barometric Pressure box at A9. This is meant to save you the hassle of converting numbers and lets Ballistic_XLR provide data for metric system users and Imperial systems without making things too complicated.
Stay tuned for Part 5.