LoadBase 3.0 Mobile w/G7 BC Test Results

[BryanLitz]

Thank you for another very meaningful post Phorwath.

I'm very encouraged to see your results working out so good using my BC's with LoadBase. I ran your conditions in the Berger Ballistics program and calculated 1611 fps of remaining velocity at 985 yards. Load Base's prediction was about 11 fps low, and the other program is about 10 fps high compared to your average measurement.

At 985 yards, the error (11 fps or 10 fps) correlates to about 1.6" of error in predicted drop. Note that a single 1/4 MOA click is 2.6" at that range.

I'll keep your results and this thread in mind to refer the next person I come across who says that ballistics programs are only good enough to provide rough estimates.

Keep up the good work.

-Bryan

 

[Pdvdh]

Bryan,
I made a boo-boo with the transcription of my recorded velocities, which has now been corrected in my original 5/2/10 Post on the 162 gr A-MAX data. Everything else was correct. Please review the Post (as updated 5/3/10) so you receive the correct conclusion. Sorry for this mistake and confusion.

Explanation for required correction: Only 1 chronograph recorded these two velocities, and not the one that was used to establish the muzzle velocity. So I was supposed to reduce my measured velocity from the PACT chronograph by ~10 fps because that's the difference in velocity I record at this distance between these two chronos (PACT & Oehler). I had increased the measured velocity 10 fps by mistake.

Now the measured 985yd velocities are adjusted properly, and the measured 985 yd velocity is 8.8 fps less than the predicted velocity. My tweak to obtain a predicted velocity matching the measured 985 yd velocity is to reduce your G7 BC from 0.307 down to 0.305.

I know I'm splitting hairs at this point. My measured velocities could off +/-5 fps, just based on the accuracy limitations of the chronographs. My laser-measured distance could be off +/- a couple yards also. I'm doing about the best I can do to obtain data about as good as my equipment is capable - but I recognize that there are inherent limitations with the equipment. And my brain - when I shift measured velocity in the wrong direction!

But I'm concluding I can run your G7 BCs with the default LoadBase 3.0 drag coefficient of 0.500 and have very high confidence that my predicted dope will be very close to dead nutz on the money.

 

[Eaglet]

Phorwath,

Very nice work indeed. I appreciate your work and your sharing with us.

Thanks!

 

[Pdvdh]

Dang! You guys may doubt my honesty if I post these results. These kind of chronograph data make me smile every time I read posts on the Forum about how unreliable chronograph velocity data are. To the point that some believe their measured downrange drops are a more accurate reflection of downrange velocity and bullet BC than a BC determined from chronograph velocities.

Anyhow - I worked up a slightly faster load that shot quite well at 295yds last weekend. Good enough that I decided I'll use the 300WM with this load for sheep hunting next month. I'm going to print out some drop charts for 10°, 20°, and 30° inclined shots. Before completing those charts I wanted to record my downrange velocities and confirm again the Berger G7 BC value was on the money.

You know the skinny by now. Here's the pertinent data, in case you LB3.0 owners/users want to ensure there's no operator error.

300 Win Mag with 25.5" Lilja 1:10 twist barrel
Berger .308 210gr VLD
G7 BC=.323
MV = 2938 fps (average of 5 shots)
Environmental Conditions: 29.75 in/Hg, 67°F, 61%RH
Default Drag Coefficient set at 0.500
LB3.0 predicted 983yd velocity = 1674 fps

Chronographed 983yd velocity = 1674 fps (average of two shots with ES of 22 fps).

My target was set up at 985 yds. The middle of the skyscreens were two yards closer. So 983 yds.

With Latitude = 60.4° and Azimuth = 90°, and Coriolis and Spin Drift turned on, the average of these two bullet impacts on target was 2" higher than the LB3.0 predicted point of impact. I'm not worried about that. No way to know the source of 2" at 1000yds, and I can't be confident that I'm any better than 2" at that range. I mostly wanted to confirm my G7 BC value was on the money. And it doesn't get any better than this!

 

[Eaglet]

I just enjoy this kind of activities. That's some mighty powerful chronographing! Awesome ballistic program too.

Did I say very good shooting?

Thanks for sharing!

I'm not worried about that. No way to know the source of 2" at 1000yds, and I can't be confident that I'm any better than 2" at that range. I mostly wanted to confirm my G7 BC value was on the money. And it doesn't get any better than this!

Agreed, I know I wouldn't complaint if it was me. Thinking about it, if 1 click = 1/4 moa at 100 yards, 1 click = 2.6" @ 1000 yards... For all practial purposes, in my book you're right on the money!!!