Ballistics Calculators / scope disagree

[Michael in California]

Help me find my error.

I'm using Strelok on my Android, but it seems to agree with on-line calculators close enough. However, my scope wants to be a full milliradian lower than calculators say.

RPR in 6.5 CM. Athlon Argos scope. Hornady 140gr ELD-M factory ammo. Chrono says I'm at about 2650 fps 10 ft out of the barrel.

Rifle is zeroed at 100 yds.

Strelok (and on-line calculators) say up 42 - 43 clicks for 600 yds. I'm about 18" high. Set scope at 33 clicks (3.3 milliradians) and I'm on the spot.

I'm afraid at this point, I only have 100 and 600 yds. I reckon I need to do some intermediate yardages to get better feel.

[randm]

Reality > Calculator. Shoot the different distances and match a BC to your real life results, especially if you can go further.
</ArmchairCoach

[ocabj]

Are you plugging in the correct density altitude into the ballistic calculator for the given conditions? Is the muzzle velocity correct?

As far as 3.3 MILs for 600 in the 6.5mm Creedmoor, that's about inline with what I have for my ballistic cards that I made for my own load (Berger 6.5mm 130gr AR Hybrid moving at 2900fps), which needs anywhere from 3.5 to 3.0 MILs up between -2000 and 15000ft altitude. I confirmed at least the 100 through 600 data to be correct.

[Michael in California]

I'm glad someone else sees the same drop. Strelok wants altitude and baro, which gives DA. MV is correct. I chronographed factory loads and the results agreed with published data.

Playing with the calculator, reasonable variations in parameters of BC, velocity, density, etc., give me back a couple of clicks, but not near 10 clicks.

[smoothy8500]

Help me find my error.

Hornady 140gr ELD-M factory ammo. Chrono says I'm at about 2650 fps

Is that number a little low? I thought it was in the 2700's

Edit: Hornady gives 2,710 fps. However, not enough difference to suggest a full Mil up elevation.

[randm]

I'm glad someone else sees the same drop. Strelok wants altitude and baro, which gives DA. MV is correct. I chronographed factory loads and the results agreed with published data.

Playing with the calculator, reasonable variations in parameters of BC, velocity, density, etc., give me back a couple of clicks, but not near 10 clicks.

Sight height, target angle, temp? Where are you shooting?

[Michael in California]

Sight height. I need to measure. I have 1.45" rings and erroneously just used that. Should be closer to 2.5". That gives me a 2.5 clicks, but that is it. Still need 7 or 8 clicks down.

Angle. Range is essentially flat. Temp is the same as the zero I set a half hour earlier at about 65 degrees. Altitude is 2200 ft.

[ocabj]

Note that my ballistic card were made with JBM Ballistics. The calculated cards were confirmed in live fire. No adjustments needed.

[Michael in California]

JBM confirms Strelok with 4 mil versus strelok 4.2 mil.

You are shooting a lighter bullet with more FPS, so 3 mil maybe right for you. Tossing your bullet into JBM without much consideration to other parameters gives 3.2 mil.

[Epaphroditus]

Elevation difference from shooting position to target?

Strelok always give me screwy numbers so I don't use it.

Scope levelled accurately? If you see excessive windage your scope is not level.

[randm]

What happens when you put 200 yd as your zero into the calculator? I tried it with the other numbers you've given (using 2.6 for sight height) and it gives 3.37mrad for 600 yds....
I'm not saying your zero is at the wrong distance-- it's just an interesting result...

[Michael in California]

Scope is level relative to rifle. I don't yet shoot with a bubble on the scope, but how far off can one be? Wouldn't matter much anyway.

Target is probably 10 ft higher than the shooting line. Negligible. 0.318 degrees.

Changing zero to 200 yds. Gives 3.6 mil. But, you really need to add the -0.4 mil to 100 yds, which gets you back to 4.0 mils.

Is my zero really at 100 yds? Measured on Google Maps, says 307 ft. Close enough.

[lwbyo1]

Another cause may be the scope itself. It may not be tracking accurately. If the turrets are giving more adjustment per click than intended, that could account for the discrepancy you're talking about. Make yourself a tracking target and see if the turret adjustments are correct.

[Michael in California]

That would be odd, but worth checking.

[RandyD]

A ballistic calculator uses a number of factors to mathematically calculate what a bullet will do after it has been fired. There are still unlimited factors that a ballistic calculator cannot consider. It cannot consider shifting environmental factors involving wind, sunlight and barometric pressure. It cannot consider the manufacturing differences in ammo, the bullets, powder lots and primer lots. It cannot consider the manufacturing tolerances in the rifle different barrels, scopes and stocks. All of those factors, and there are more, affect the flight of the bullet. A ballistic calculator will put you on target, but it does not guarantee a dead center hit for every shot. This is why you need to test your rifle, loads and improve your skills.