Trajectory Validation: Ten Steps for Success
Trajectory validation is the final step for building confidence in a long range precision rifle. Also known as drop truing, it’s the process of tuning a ballistic solver to a scope, rifle, and its ammunition. Its sole purpose is to allow a cold bore, first round hit on a target.
As I was swinging my Kestrel Elite in the air to clear the temp sensor wire, I knew I was going to score a hit on the rock 1809 yards away. An hour before, I’d logged first-round hits on rocks at 490, 1001, and 1147 yards. Not just hits, either. Center-of-the-rock hits. The kind of hits that make you feel good. Three shots from the 300 WM later, I decided the wind would be the winner today. I just couldn’t time the three-second flight of the bullet to coincide with the surge up the canyon. They all hugged the right side of the rock, landing in a sub-MOA group with a perfect elevation correction. A good spotter is worth more than the best trigger-puller in conditions like that. I knew the solver was giving me good corrections, though, and that’s what I was after.
With two rifle projects running simultaneously, trajectory validation is something that’s been keeping me busy. I’ve fired enough shots from both of them now to have complete confidence in my ballistic solvers for any shot my rifles are capable of.
How to make a ballistic solver match up to what the actual long range drops are is always in the top three of questions I get about long range shooting. Here are ten things I do to make it work every time:
Zero the rifle perfectly.
This is the number one mistake I see shooters make. A perfect, repeatable zero is absolutely essential to hassle-free trajectory validation. It’s the foundation that all other corrections are built on. It’s worth saying again—not only does the zero need to be perfect, it needs to be repeatable. If your scope won’t hold a zero, you need to isolate why and fix it. I use a 100 yard zero to minimize environmental factors affecting the bullet and check it regularly.
Use an accurate chronograph to measure muzzle velocity.
There seems to be a trend of shooting to a measured distance and using the actual bullet drop to estimate muzzle velocity. It’s certainly a quick way to find a velocity number to plug into the program, but it doesn’t necessarily tell us what the true muzzle velocity is. What if the muzzle velocity is different on a cold bore shot, or fluctuates with temperature swings? How do we determine our ammo’s Extreme Spread (ES) or Standard Deviation (SD)? What if you change the load, or your barrel speeds up or slows down? I will also add that if you don’t know what the true muzzle velocity is, you can’t know why your drops don’t match your ballistic solver’s corrections.
These variables are much easier to measure and account for with a chronograph than shooting at distance. I own an Oehler 35 and a second-generation MagnetoSpeed. I trust both of them, but have been using the MG a lot lately because of its convenience. I highly recommend it.
Make sure your scope’s turrets travel the correct amount and use a scope level to avoid canting.
Plumb the vertical stadia of the crosshair to a scope level, and do a tall target test to check the scope’s travel up and down as you dial the turrets. Do this at the same distance your rifle is zeroed and be sure it returns to zero when done. What you’re looking for is the amount of travel the turrets provide for any given correction. If you dial up 20 MOA but the impact only changes 19.5 MOA, you need to know that before trying to validate and see if you can fix it. Canting the rifle can cause that, as can a faulty scope.
This is the number one reason I recommend Nightforce NXS and ATACR scopes. I have never had one not dial the correct amount and they always return to zero. Period.
Use an accurate bullet Ballistic Coefficient (B.C.)
Bullet manufacturers are getting better at providing accurate B.C.s, but it still doesn’t seem to be an exact science. In my experience, they’ve been accurate enough for long range hunting distances. The recommended drag model is G7, but I’ve had good luck with G1 as well. I’ve never used a custom drag curve, but they’re available if you use Applied Ballistics.
Before you mess with adjusting B.C.s, make sure your zero is perfect, muzzle velocity is accurate, and environmental conditions are entered correctly. I’ve used Berger, Hornady, and Sierra match bullets out to 2000 yards and can’t remember adjusting the advertised B.C. for any of them. Unless you’re shooting to distances that require drop scale factoring, stepped B.C.s, or other advanced tuning, adjusting the muzzle velocity input is the way to go.
Remove as many variables as possible.
Trajectory validation in hard to read conditions is just asking for trouble. The wind can have an elevation effect as well as left or right. Steep hillsides that face into a brisk crosswind can have a dramatic influence on bullet lift. Some ballistic programs account for crosswind jump, but most don’t. I like to true drops during the calmest conditions possible.
Just like this shouldn’t be a time for big wind practice, don’t try new positions during trajectory validation. Use a solid prone position and make it as easy as possible to make that perfect shot.
Don’t try to validate in heavy mirage.
Sooner or later, you’re going to be faced with shooting through a boiling sight picture, but attempting it during trajectory validation is pure folly. Mirage changes our perception of where the crosshairs lie in relation to the target. I don’t try to zero or validate drops with heavy mirage. Early mornings, late evenings, or overcast days are best. They also tend to be the calmest times to shoot.
Master the operation of your ballistic solver and use accurate environmental inputs during trajectory validation.
Spend some time with your ballistic solver before validating drops to be sure you understand how it works. Some solvers are more complicated than others and options for trajectory calculations can vary. Study up on Coriolis and spin drift and how they affect long range bullet flight. As usual, the longer the distance the more these things matter.
Station pressure, temperature, and humidity should be measured carefully. I will concede that small discrepancies for most shots don’t matter, but because we’re checking our trajectory toward or in the transonic area of the bullet’s travel, even the smallest variables can make a difference. Use a Kestrel weather meter to measure these inputs precisely during trajectory validation.
Trajectory validation should be done at a distance that makes sense.
Validating at short distances won’t always work for shooting long distances. Ideally, you would check the trajectory to the distance where the bullet’s velocity is transonic. I start validation at 700 yards and gradually extend that range to 1800 yards or more. I don’t hunt at extreme distance, but I validate for it and practice as far as my equipment will let me. Get out there and stretch its legs. It will make the closer shots seem easier if you work on the longer ones.
Be realistic with your accuracy expectations.
Get all of the bugs worked out of your long range load before you start validating. To save time, I’ve tested the long range accuracy of a load while also doing initial trajectory validation, but it can be frustrating if the load doesn’t work as well for long range as it did for short range.
It takes a lot of precision for a rifle and ammunition combination to consistently hit small targets at any distance, but the further away the target is, the more that precision matters. When you factor in the accuracy of the optical system, the shooter, and reading conditions, that precision might suffer a little. It’s been my experience that good barrels that consistently shoot < .5 MOA at 100 yards will hold that precision at long range. If you have problems with consistency or accuracy at extended distance, check it again at a shorter range. If it checks out, you may need to revisit your load recipe. In particular, the bullet it uses.
I typically fire two consecutive rounds when truing drops. No need to fire groups, but consistency should be checked. There’s usually enough time to fire two rounds before conditions change that could affect the trajectory. Fire enough rounds at that range to be confident with the correction then find another target to engage. For a good example of this, watch this video.
Conditions on any given day will dictate how much accuracy to expect, but what we’re looking for during trajectory validation are vertical discrepancies. Targets should be suitable for accurate impact calls with enough area to see rounds that don’t hit in the center. Around here, I like to shoot at granite faces that sprout from our mountains. I try to find one that’s at least 2 MOA square with a precise aiming point. Large steel plates that are painted white would be my second choice.
Take the time to get it right and record your data.
Just like perfecting your zero, take special care to make the first shot count. Long range hunting is typically a one-shot deal, so that first one needs to be right. If the trigger didn’t break cleanly or your sight picture wasn’t perfect, repeat the shot. Learn how to call your shots, and follow through after the recoil to spot the hit. An experienced spotter and/or a video camera to record shots can help a lot with trajectory validation.
I log all shots taken during trajectory validation in a simple data book that stays in my shoot kit. I record environmental conditions, estimated wind call, actual wind correction needed, and elevation correction. If I have to adjust the velocity in the solver to match up with the correction, I note how much and highlight it. It’s been my experience that if I have to adjust more than 10-20 fps, I need to look at my zero or scrutinize my ammunition.