How accurate are ballistic calculators?

[heffsdm]

How accurate are ballistic calculators expected to be, specifically with regards to elevation? For me, the actual point of impact is about 1 MOA high at 200 yards when dialing for the ballistic calculator's predicted bullet drop.

I'll be shooting out past 500yds for the first time in a few weeks, so I used Berger's ballistic calculator to give me an idea of what I should dial for elevation at various distances (I'm shooting 140gr Berger Hybrids from my 6.5 creedmoor). To double check the calculator, I went out to the range today and with the scope zero'd at 100yds, I dialed up 0.5 mils and fired a couple shots at a 200yd paper target (the ballistic calculator predicted a 0.47mil drop at 200yds). However, I could see that this put my point of impact much higher than expected.

I used the scope's reticle to measure the difference between point of aim and point of impact, which was 0.3 mils, or about 2" (after I later retrieved the target, I measured the difference between the POA and POI to be almost exactly 2"). So I dialed my elevation turret back by 0.3 mils and impacted just at the bottom of the 1" square I was aiming at. Shot a 5-round group, and everything looked good.

Having never used a ballistic calculator before, maybe being off by 1 MOA is normal and I'm overthinking it. It was certainly good enough to get me on paper, but I was expecting it to be much closer than it was.

Some sources of errors that I've considered:

1. Incorrect velocity entered into the calculator. I'm using hand loads and I have a magnetospeed, so I have a pretty good idea of my actual velocity at the muzzle. When I saw the above discrepancy at the range, I threw the magnetospeed on the barrel and fired 15 shots which gave me an average velocity of 2679fps. I had entered 2680fps into the calculator, and double-checked to make sure I hadn't typed the wrong number into the calculator.
2. Magnetospeed measurements are incorrect. According to the ballistic calculator, I'd need to be getting around 3,000fps at the muzzle in order to match the actual elevation drop I saw at the range. Even if the magnetospeed is somehow faulty, I don't see how I'd be getting that speed with a 140gr bullet and 40gr of H4350.
3. Published BC doesn't match actual BC. I played around with the bullet's BC values in Berger's ballistic calculator, and even significant changes to the BC had minimal effect on the predicted drop at 200yds.
4. Scope turrets don't track. I have a Nightforce SHV, which I know isn't a top-of-the-line scope, but it's not a $100 scope either. Not to mention that when I measured the elevation drop in the reticle and then dialed that drop on the turret, it worked fine. This is also how I zero'd at 100yds and had no issues there either.
5. Berger's ballistic calculator is wrong. I tried another online ballistic calculator which gave me the same numbers as Berger's.
6. The distance I'm shooting at isn't actually 200yds. It's advertised as 200yds and it looks like 200yds to me, but I don't have a range finder to verify that. The elevation drop I'm seeing is more consistent with the elevation drop of a target somewhere between 150-175yds, according to the ballistics calculator. The range is run by a local gun club so it's not just some targets set up in Billy-Joe's back yard, but maybe it's just a matter of false advertisement.

Just wondering if there's something I've overlooked or done incorrectly, or is 1 MOA at 200yds not an abnormal error?

 

[clcustom1911]

So, your impacts are 2.094" high at 200 yards? It could be a shooting position issue as well. Your stock could he slipping down just a smidgen causing the rounds to land *this* much higher on target.

Measure your scope height as well. If you have 2.5" entered into the calculation, but the actual height is, say 1.9", that would cause your impacts to be higher because your calculations want to adjust higher to make the impact jive with reticle height at that distance.... I think ? or the reverse of that..... either way, make sure your scope height above bore measurement as accurate as you can get it. I've played this game once because I was a retard and just eyeballed it.... once I measured things correctly, I was much more consistent out at distance.

I too have a magnetospeed, and I still verify my velocities at 300 whenever I'm truing my load.

 

[Precision Underground]

They are exactly as accurate and complete as the data you input into them.

 

[Precision Underground]

Make sure your scope height measurement is correct. That’s a big one that can throw off your solution.

 

[Dthomas3523]

You haven’t trued your calculator to your rifle.

No need to wander off on 18 tangents on why it’s not 100% perfect out the gate. Make sure all the data you entered is correct and the use whatever truing process your calculator allows.

MV, BC, bore height can be tweaked to make your data line up.

 

[heffsdm]

Thanks guys, I did measure my actual sight height when using the calculator by taking the radius of the bolt and the radius of the scope (measured the diameter of both with calipers) and adding that to the distance from the top of the bolt to the bottom of the scope. I'll definitely double-check that, but playing around with the numbers in the calculator it looks like I'd have to be off by an inch or more to get the numbers to match up.

I think @clcustom1911 may have hit the nail on the head. I forgot my rear bag when I went to the range so I used one of the sandbags that the range provides...which was wrapped in duct tape. Very possible it was just a matter of the buttstock slipping during recoil. My groups were good so I hadn't even considered the effects of the shooting position. I guess I'll have to go shooting again to verify...oh darn. ?

 

[clcustom1911]

@heffsdm

I only know because I regularly screw up. Knowledge and good judgment come from mistakes and bad judgment ?

 

[GIXXER2000]

There are a lot of options when it comes to ballistic calculators. The ones you can get as an app work well for most shooters. I shoot ELR so i run Field Firing Solutions on a Trimble Nomad 900 series hand held. It is a very good system but does require time and effort to learn to use it.. As far a accuracy I cold bored the 2625 target at my last ELR shoot. I have spent the time to true the BC and my Kestrel meter. I know the that the Applied Ballistics program is also very good. The other IPHONE apps from what i have seen work well out to about 1500 yards. It just comes down to how far do you need you program to be accurate.

 

[b6graham]

are your 100 and 200 yard lines verified exact?

 

[hereinaz]

Ballistic calculators are not perfect, but I don't think that is it. I get .4 mils for my solution with 140s. They are algorithms that use models to predict how a bullet will act. That is why every ballistic solver really needs to be trued to reality. Now, you can do things to improve the prediction and some solvers are better than others. But, they are not perfect. Go listen to the Everyday Sniper Podcasts, and you'll regularly hear Frank talk about the limitations of solvers. In my experience, using Applied Ballistics solver with the custom drag models are very close.

That being said, seems like 2 inches is pretty far off for the ballistic solver to create that error. I would find it hard to believe that the rear bag would cause two inches at 200 but nothing at 100. If you were zeroed and shooting at 100 with the same conditions, I would not think it was the bag. I could be wrong.

BC won't affect the solution that much.
Velocity would have to be way off.

Until you verify the distances of the yard lines, that is what I would go with. If your 100 yard zero is not really 100 and the 200 yard line closer, you would get the sort of errors.

I would shoot at both yard lines, without touching the turrets and then measure the drop. That will tell you some information without the possibility of the scope turrets being off, but I have a hard time believing they would be off that much.

My bet is on a combination of a few things, like distances to the targets, zero not perfect, and maybe the rear bag.

I once entered the zero range in feet on my Garmin, cause the button you push ran so fast I missed that it went from yards to feet. Want to talk about being confused...

 

[captainmorgan460]

Shooting position variances and range variance as described above is what I would say. Quick look at a table, and roughly if the 100 yard target was 90 and the 200 yard target was 240 that would produce the difference you're seeing.

Applied ballistics is usually fairly accurate to start, seems like for me once I have a few velocity averages across a temp range things start to work out better.

 

[heffsdm]

Thanks for the input, all! I'm going to head back to the range tomorrow to double check my 100yd zero and the bullet drop at 200. If I still have the same discrepancy, I have access to another range which would help to rule out (or confirm) the theory that the 100 and 200 yard targets aren't actually at their advertised distances.

 

[heffsdm]

The issue was my 100yd zero. Double checked my zero and was about 1" high at 100yds, which makes 2" high at 200yds make perfect sense. Not sure how that happened, but I re-zero'd, dialed the calculated drop for 200yds, and it was spot on.

 

[FLhog]

They are exactly as accurate and complete as the data you input into them.

Indeed. Someone once told me “Garbage in, Garbage out”.