My actual drop for the last three loads in multiple rifles is always more than what multiple different ballistic calculators say. About 3-4 moa off. I don’t think it is my chronograph. If anything, loads are typically slower than expected over it. How accurate is your loads compared to the calculators?

Same projectiles? Have you checked Bryan Litz' calculated BC for that projectile?

Have you tried calibrating the MV in the ballistic calculator?  Most of the time the calculator will get you close and then you have to refine it at the transonic range, to get a accurate hold.

The loads are for hunting with Leupold and Vortex bullet drop reticles. I was hoping a calculator would be close so I could test the loads at 1000 feet of elevation then use them hunting at 6000 feet. They use Speer SP, Nosler Partition and Nosler Accubond bullets.

I have tried these calculators,

Shooters calculator.com
Sierra program
Nightforce program
Hornady's calculator

They all agree with each other within an insignificant amount of error.

Maybe I am putting too much faith in the reticle drawings and accuracy of the magnification of the scopes that affect the reticle size. The error is more than Parallax error and group sizes are very good.

If they're second focal plane variables with mil/moa scale reticles then you're not at the correct magnification for the reticle scaling. If you're putting good data in then the way you're using the optic is busted. If you're putting bad data in then the way you're using the calculator is busted. The math doesn't lie. Some manufacturers are a little optimistic with BC's but not usually by enough that you'll notice inside 700yrds.

OP, have you ever ran a tall target or box test on your rifle/scope? they are designed to check that your knobs/scope/reticle is moving the amount it says it is..Basically, you are going to make/use a calibrated target set for your system(MIL/MOA) to shoot at exactly 100 yards to check that the movement of the knobs/reticle/spacing all function as designed..the tall target checks elevation, the box test windage..(I combine them all in one target)by aiming at one single point for the entire test while adjusting knobs and making sure the bullet impacts at the correct distance as dialed...you go up/down/around the target and return to the aim point(zero) at the end...




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Are all your variables accurate. Height over bore For example is important as well as your coefficient.

IME, the calculators are accurate, my chrono is accurate, my bullets bc should be accurate. For the brand conscious, AB Kestrel, Labradar, Berger EH….

That said, zero a calculator needs trued to what is actually going on. In simple cases adjusting zero offset can fix things. Then MV, and sometimes BC needs trued.

I find if you are already a click or 2 off at 300-500, I would start by adjusting zero offset. Then in the intermediate drop range, adjusting MV can help, finally sometimes bc needs adjusted, even for Bergers.

The key is getting good drops and wind holds, then tune the calculator to match reality.

For scopes with lots of MOA of forward cant and a long barrel/short scope vs a short barrel and longer scope the height over bore can be measured differently by at least 0.1" by the end user. Two people might also be 0.1" off on the same optic when they measure. Often shooters are off by 1-2 clicks on their 100y zero, sometimes because they zero at 95 yards at a local range, etc. I would start with a 0.1-2" optic height shift in your ballistic computer, tune 1 click elevation for zero, then tune G7 BC depending on bullet, then tune velocity last.

How are you getting your environmental data? Is your ballistic computer accounting for aerodynamic jump? What reticle and scope are you using? It all matters, but 3 MOA off at 300 or 500 sounds like a large data input error combined with a zero error.

Another zero error is zeroing with a small incline or decline. The three common zero errors COULD add up to three clicks of zero error. (Wrong distance for 100y zero, angle of incline to 100y zero, and final decision which is the "best" between two elevation clicks.)

Other than that it is probably chronoing in the summer and shooting in the winter. Can't think of much else. Unless you are using the same G1 BC for 100-300 and 600+ yards.