I’ve laid the foundation for the primary learning point of this two part article in the previous article titled, “My Approach to Hand Load Development.” Now comes the ballistic truing part. External ballistic truing is simply the act of tweaking the muzzle velocity in your ballistic software to correctly reflect what you saw at the rifle range. We do this to ensure that we have a good adjustment to put us on target at new target engagement distances. This makes gathering ballistic data a much shorter day at the range. Additionally, as soon as your ballistic profile is true in your software, you can use that final muzzle velocity and ballistic coefficient to create a windage chart, temperature change chart, altitude change chart, and air pressure change chart custom for your own rifle and pet load. The 41.8gn load from the previous article performed best at 290 yards for me given a 1.0gn spread from 41.0gn to 42.0gn of H4350 rifle powder. This 41.8gn load impacted .941 inches high on target at 290 yards with an adjustment of 4.0 MOA.
How high above my 4.0 MOA adjustment in MOA did the group impact?
Inches / Range in Hundreds / 1.047 = MOA
.941” / 2.90 / 1.047 = .31 MOA high on target
What new adjustment would put me center-center at 290 yards?
4.0 MOA – .31 MOA = 3.69 MOA
Instead of 4.0 MOA, 3.69 MOA would be the perfect adjustment for this load at 290 yards. Hornady reports their 6.5mm 140gn A-Max to have a ballistic coefficient of .585 BC, so we’ll keep this in our software. We will need to tweak the muzzle velocity in our software until the 290 yard report equals 3.69 MOA. What we WILL NOT do is tweak the M.V. to a rounded number like 3.75 MOA. At this short distance, we’ll be exact. Before leaving the range, we’re sure to record the actual environmental conditions that we shot in. I use a wrist Garmin and a Kestrel weather meter to get these numbers. The environmental conditions of that day follow:
Angle: 0 degrees
Wind: 2mph full value
Elevation: 320ft (ground elevation… GPS reading)
Altitude: -10ft (pressure altitude… This is the one that your software understands)
Temperature: 40 degrees F
Air Pressure: 30.27 inHg
Humidity: 70% RH
By inserting the above environmental conditions into our software, and tweaking the muzzle velocity in our software, we get exactly 3.69 MOA of required elevation at the 290 yard mark with a muzzle velocity of 2710fps. We’ve just trued our ballistics for this load.
So what can we do with this information? Well, we can be on target at distances we haven’t fired at yet by simply setting our ballistic software to report MOA adjustments out to 1,000 yards in 10 yard increments. We can effectively engage ranges closer than 300 yards and farther than 300 yards despite never having attempted those ranges yet. These rounds will be on target although will normally be up to 1.0 MOA high or low from our point of aim as a result of truing the ballistics at such a short distance. Upon shooting at farther target ranges, we would of course take the target home, measure how high or low the rounds impacted in relation to the point of aim, and true the ballistics yet again. Always true your ballistics at the farthest target distance available and accurately record the weather conditions that you fired these shots in. I’ll undoubtedly find that in order to keep my 3.69 MOA, 290 yard elevation requirement in the software while at the same time truing my—say 600 yard—data, I’ll have to also adjust the ballistic coefficient of .585 BC to a slightly different number… Not just the muzzle velocity. The expensive ballistic software will do this for you. It will true your ballistics at the multiple distances that you’ve fired and gathered known data from, by adjusting the muzzle velocity and BC on its own. I however don’t mind taking the time at home to punch the numbers in myself on the $10 verson.
Having read these two articles, you likely legitimately care to learn and understand this information at this level. And I hope that it was perfectly clear for you. I’ve done rifle instruction enough that I recognize that despite how concretely I believe I’ve presented these facts, there will always be questions. In my book Long Range Precision Rifle Success: the Complete Guide to Hitting Targets at Distance, I included an email address at the back of the book which readers can use to pose questions directly to me during their learning process. The great thing about this website is that as you go through the articles, you can post questions if you reach any points of friction in learning. Those learning on this website are all at different levels of proficiency. Don’t be afraid to post questions. We’ve all been new to this style of shooting at some point. I’m constantly in learning mode myself. Additionally, I urge anyone with subject matter knowledge specific to this topic to provide your “two cents.” If I’ve missed anything that can facilitate better understanding for readers, feel free to add to what I’ve stated here.
Keep ‘em in the X-Ring!
Anthony J. Cirincione II is a U.S. Army sniper and avid precision rifle and long-range rifle shooter, competitor, and enthusiast, as well as a member of the National Rifle Association and the American Sniper Association. He is the author of the book, Long Range Precision Rifle: The Complete Guide to Hitting Targets at Distance. This book was written to provide U.S. military, U.S. coalition forces, and local law-enforcement personnel with a tool that they can use to properly set up their rifles and optics, and effectively employ them out to their maximum effective target engagement ranges. Having omitted certain tactics, techniques and procedures that can potentially pose a threat to the operational security of our professionals, this book is unclassified, and is available to the law-abiding citizen.