Range Report Wild dope truing AB and 4dof. What is reasonable?

[OREGUN]

To get impacts beyond 600 yards, I’m having to change my bc from .292 to .280 AND change MV from a twice verified (two garmins running side by side) 2770 to 2750. On the Hornady app, this equates to 2750 and a AFF of 1.10. If I don’t change the muzzle velocity, there is no allowable AFF large enough to give me true results. To clarify, if I put in the largest allowable AFF and start lowering MV, 2750 is the first speed at which the calculated dope matches reality after conventional rounding. The curve predicted by AB matches at .280/2750. If I put the verified MV (2770) in to AB, i have to go to a BC of .272 to get hits.

This is verified at both 1800 ft and 70* and 7000 ft and 40* on small enough targets that I’m confident it’s not just bad shooting/spotting.

Berger 109 LRHT, 7.5 twist. 1000 rounds on the barrel/brake combo. 30 rounds over the garmin shows an SD of 8 and an ES of 34 and the barrel shot two back to back cloverleaf groups (sub 1/2”).

Anyone have any ideas why I’m seeing such incredible inefficiency downrange. Something about the bullets? A barrel problem causing a change to external ballistics? I’ve never seen such a huge truing solution required.

 

[kilizyrag]

Someone please answer this. I wanna know the outcome.

 

[021411]

I’ve had MV and BC change pretty drastically but that’s what truing is. You’re just telling the calculator what your bullet is actually doing. At that point I don’t care what the numbers are as long as I’m impacting steel or whatever said and done consistently.
It’s how Gravity Ballistics works as well. It doesn’t care about anything else but actual impact data.

 

[OREGUN]

Current best guess and working theory is a terribly inefficient lot of bullets. Oddly, if I change the bullet to the 105 hybrid profile and use actual MV, the dope lines up just about right.

I don’t care about the numbers either, I’ve just never had to go to such extremes.

 

[kilizyrag]

Current best guess and working theory is a terribly inefficient lot of bullets. Oddly, if I change the bullet to the 105 hybrid profile and use actual MV, the dope lines up just about right.

I don’t care about the numbers either, I’ve just never had to go to such extremes.

Curiosity is killing me. What inefficient lot of bullets; brand?

 

[jyeager]

Current best guess and working theory is a terribly inefficient lot of bullets. Oddly, if I change the bullet to the 105 hybrid profile and use actual MV, the dope lines up just about right.

I don’t care about the numbers either, I’ve just never had to go to such extremes.

Is this speaking of 4DoF? Maybe their bullet profile for the 109 LRHT is wrong. Or maybe you didn't get the bullets you thought you did (perhaps even the wrong ones in the right box). If you have to modify your axial form factor more than 10% from 1.0 they say something is wrong.

 

[JAS-SH]

To get impacts beyond 600 yards, I’m having to change my bc from .292 to .280 AND change MV from a twice verified (two garmins running side by side) 2770 to 2750. On the Hornady app, this equates to 2750 and a AFF of 1.10. If I don’t change the muzzle velocity, there is no allowable AFF large enough to give me true results. To clarify, if I put in the largest allowable AFF and start lowering MV, 2750 is the first speed at which the calculated dope matches reality after conventional rounding. The curve predicted by AB matches at .280/2750. If I put the verified MV (2770) in to AB, i have to go to a BC of .272 to get hits.

This is verified at both 1800 ft and 70* and 7000 ft and 40* on small enough targets that I’m confident it’s not just bad shooting/spotting.

Berger 109 LRHT, 7.5 twist. 1000 rounds on the barrel/brake combo. 30 rounds over the garmin shows an SD of 8 and an ES of 34 and the barrel shot two back to back cloverleaf groups (sub 1/2”).

Anyone have any ideas why I’m seeing such incredible inefficiency downrange. Something about the bullets? A barrel problem causing a change to external ballistics? I’ve never seen such a huge truing solution required.

There is a lot of stuff involved in trajectory calculations. You miss a step and they wont work at longer ranges.

I use Hornady's 4DOF and find that it's very accurate to +/- .01 adjustment factor (so .02overall) in the app. The key is to get a REALLY good (very high confidence) zero in very accurately measured conditions. And that all starts at 100 yards. Conditions will change further out but at least you can get very accurate conditions and zero measurements, and its not that easy. Doing that I can be on the "waterline" at 600 - no issues, meaning left or right is just wind.

Another thing I've found is that measuring really accurate conditions at 100 and then going to 600, the software is doing its job, but not if there are environmental differences that I miss. Wind is one of them of course - If I don't input the wind correctly at my 100 zero and specifically wind from 0 or 180 degrees, everything else could be correct and the impact point is different. And obviously, conditions can change during the day, sometimes drastically.

Calculators wont make you shoot better, that comes with experience. Armed forces snipers record all parameters for every shot they make. Over time that becomes a huge library of information that still to this day offers better solutions than calculators. And it's usually a 2-man team which makes that easier. Sniper teams DO use calculators. That said they know from experience how to make adjustments to the calculator solution.