Range Report Ballistics Results from Using Lapua Radar Data

[wadebrown]

Comparing Ballistics Calculations Using Litz’s BC and Lapua Radar Data

Lapua’s radar data available on their website opens up some interesting possibilities, for ballistics calculations we may not need to rely on BC’s and directly use the drag curves offered by Lapua.

I added the drag curve for 6.5 mm 139g Lapua Scenars into my ballistics solver, I chose this bullet as I shoot more 6.5mms than any other. My ballistics solver uses the same methodology as the one Bryan Litz includes with his book and it tends to match both Bryan’s and JBM’s solver. prior to writing my own solver I used JBM and found it to be very good so I use that as a benchmark to test my solver, I also use range data and Bryan’s solver.

The intent was to see what the compare the calculated results for three methods, my solver with Bryan’s G& BC and with Lapua’s radar data and then use JBM’s solver with Bryan’s G7 BC. Here are the results

Wade's Solver JBM
Range Speed Drop Litz Drop Radar Drop Litz
(yds) (ft/s) (inches) (inches) (in)
0 2750 -1.5 -1.5 -1.5
100 2591 0 0 0
200 2435 -3.69 -3.7 -3.7
300 2284 -13.26 -13.33 -13.3
400 2139 -29.51 -29.71 -29.6
500 2000 -53.38 -53.83 -53.5
600 1865 -85.97 -86.8 -86.1
700 1734 -128.6 -130.21 -128.9
800 1608 -182.83 -185.52 -183.3
900 1486 -250.56 -254.81 -251.2
1000 1369 -334.11 -340.56 -335

The third column is my solver with Bryan’s G7 BC, fourth column is my solver using Lapua’s provided drag curve and the final column is JBM’s solver using Bryan’s G7 BC. I included the JBM result to show that my solver which none of you have seen is close to JBM’s which many of you have experience with. The largest difference is at 1,000 yards (no surprise) and this is only 0.62, so it would take a better shooter than I to shoot and be able to tell the difference between the results calculated with Bryan’s BC or Lapua’s drag curve from radar data.

As Bryan Litz pointed out in an earlier post the radar data may give us an indication of what bullets cross the transonic gracefully.

I editted it to clean up the format of the table so it was easier to read.

 

[BLAWTON]

Re: Ballistics Results from Using Lapua Radar Data

My friend starting messing with the 300 grain lapua bullets. We took their data and hit within 3" of point of aim and 1500 yards... I think the stuff is spot on!

 

[TiroFijo]

Re: Ballistics Results from Using Lapua Radar Data

Just for grins...

Using Sierra Infinity (I'm sure JBM is reaaaaally close) and a <span style="font-weight: bold">G1</span> BC of 0,542

std. conditions, 2750 fps muzzle velocity

range Sierra drop Radar drop
(yds) (inches) (inches)
0 -1.5 -1.5
100 0.0 0.0
200 -3.7 -3.7
300 -13.4 -13.3
400 -29.8 -29.7
500 -54.0 -53.8
600 -87.1 -86.8
700 -130.4 -130.2
800 -185.7 -185.5
900 -254.9 -254.8
1000 -340.0 -340.6

 

[Lindy]

Re: Ballistics Results from Using Lapua Radar Data

No one so far has stated what they used for atmospheric conditions, so I can't check those results against the other ballistic programs I have, including Bryan's.

My experience leads me to suspect that all will differ from field shooting data, though...

 

[BryanLitz]

Re: Ballistics Results from Using Lapua Radar Data

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">std. conditions</div></div>

Out of curiosity, what are the std. conditions defined in Sierra Infinity? Are they the same std. conditions defined in JBM? I thought Sierra uses the ASM atmosphere model (59deg, 29.53inHg, 78%RH), and JBM uses ICAO (59deg, 29.92inHg, 0%RH).

If you got the same trajectory using different models of standard atmosphere, there's something to say about that.

Curious,
-Bryan

 

[wadebrown]

Re: Ballistics Results from Using Lapua Radar Data

Sorry I dod not include the atmospherics. I used the following both JBM's and my solver and they are:
Temp 60°F
press 30.10 in Hg
40% rel humid
0% humidity
an oddball one that I used for some other testing.

 

[Lindy]

Re: Ballistics Results from Using Lapua Radar Data

You listed two figures for humidity. Which did you use?

 

[TiroFijo]

Re: Ballistics Results from Using Lapua Radar Data

Bryan, you know that these small variations in "std. conditions" mean VERY little out to 1000 yds... in this case about 4.3"

My observation was just to show how little difference makes using the G1 drag model when calculating inside the supersonic range. Of course, if you only have a couple of data points to estimate your BC it is better to use the drag model that fits better (even if by a small margin), but if you fit your computer model to extensive field data as suggested by Lindy (and preferred by me) you can use the G1 model and get a very good fit.

Again, using Sierra Infinity and a <span style="font-weight: bold">G1 BC of 0,552</span> (tweaked to match the Lapua radar data)

JBM std. conditions (59deg, 29.92inHg, 0%RH), 2750 fps muzzle velocity

range Sierra drop Radar drop
(yds) (inches) (inches)
0 -1.5 -1.5
100 0.0 0.0
200 -3.7 -3.7
300 -13.4 -13.3
400 -29.8 -29.7
500 -54.0 -53.8
600 -87.0 -86.8
700 -130.4 -130.2
800 -185.7 -185.5
900 -254.8 -254.8
1000 -340.1 -340.6

 

[wadebrown]

Re: Ballistics Results from Using Lapua Radar Data

40 although I think humidity is the least sensitive variable. The absolute values are not the big issue what I was trying to show that in that area of velocity the differences between the models (Lapua Radar or Bryan's G7) is little and for someone of my shooting ability un testable in that regime.

 

[BryanLitz]

Re: Ballistics Results from Using Lapua Radar Data

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Bryan, you know that these small variations in "std. conditions" mean VERY little out to 1000 yds... in this case about 4.3" smile

My observation was just to show how little difference makes using the G1 drag model when calculating inside the supersonic range.</div></div>

T,
I was asking about atmosphere models because it can make a difference in the predicted trajectory; ~3"-4" at 1000 yards as you mentioned. This is just something to consider when inputting a BC into a ballistics program. If the program assumes you're giving it a BC that's corrected to standard ASM atmosphere, and the BC is really defined in relation to the ICAO atmosphere, you incur an error of about 1% to 2% in BC. You were displaying a match between two programs that use different atmosphere models, and that's why I mentioned it.

Atmosphere aside, let's consider the match between a G1 trajectory and the trajectory predicted by the radar data.
First, I acknowledge your demonstration that you can find a G1 BC that results in a close match for a given range. However, consider the following:
1) The G1 BC you found is unique to 1000 yards. If you wanted a G1 BC to best match a 1200 or 1500 or 600 yard trajectory, it would be different.
2) The remaining velocity predicted by the G1 BC will be far different than that predicted by a G7 BC or radar data. Typically, the G1 BC will way over-predict the remaining velocity at range. This is important for those who care about striking energy (lethality) and remaining supersonic at some distance.
3) The time of flight, and calculated wind deflection will be off. I don't consider this to be a major problem given the uncertain nature of wind speed/direction to begin with.

If you 'tweak' the G1 BC to match the radar predicted velocity, the drop will be off. If you tweak it to match the drop, the remaining velocity will be off. If you tweak it to be a 'best fit' for a certain range, it will be off at other ranges.

The amount of error you incur by using G1 BCs can be more or less significant depending on your application. If you're just trying to get some sighters on paper in a competition, it's plenty good. If you need a first shot to be in the vitals, it's advisable to use the best model that's available.

And regardless of the drag model you use (G1, G7, radar, etc), one should consider what standard atmosphere the BC is corrected for, and what the program assumes.

Take care,
-Bryan

 

[Ewen]

Re: Ballistics Results from Using Lapua Radar Data

Hi all, just for shits and giggles I punched in this data to Load Base to see what it comes up with. I was kinda shocked at the results.

Using the same data as initial post and the BC from Mr Litz book.

BC (G7)= 0.285 (page 416 of Litz’s book)
DC= 0.500 (default)
MV= 2750 fps
SH= 1.5 inches
ZR= 100 yards
ICAO Std Conditions


Path at 1000 yards

Radar= 340.56 inches
LB3D/M= 339.60 inches
Diff= 0.96 inches (0.09 MOA)


Interesting to me is how it matches so well without fudging the BC. I know Tiro managed to match the path but only by moving the BC to somthing other than the correct. This is cool however is not mutch use for shooting without a lot of prior testing in order to match the curve.

Ewen

 

[TiroFijo]

Re: Ballistics Results from Using Lapua Radar Data

Bryan, in the trajectory comparison I showed the very good <span style="font-weight: bold">drop</span> match of a tweaked G1 BC to the radar data. The comeups in MOA are identical at all ranges, and it took me about three minutes with a basic program. If the sight height is constant (as is our case) then <span style="font-style: italic">if the drop at any range correlates with the radar data the trajectory is going to be the same</span>, no matter if you zero at 200 or 600 yds.

Now, of course you need the radar data or trustworthy field data from 0 to 1000 yds (in 100 or 200 yds steps) to play with the program and match it.

There might be <span style="font-weight: bold">minor</span> errors in TOF, velocity, and wind deflection, but as you said given the nature of the changing winds donwrange this is hardly of any consecuence

Now, this is just one example of a VLD bullet that shouldn't match the G1 curve, yet the BC can be tweaked to match. Not all bullets are going to match it so well, but if in general if you take the G1 BC (or match the trajectory) over the maximum supersonic range, or at least 80-90% of it, the error is going to be very small at all ranges, normally max error is less than 0.5 MOA, and only in a few points. Since very few people can shoot into 0.5 MOA, and even less can determine in the field with no doubt that the POI error is not due to other evironmental causes, these errors are small.

 

[JL]

Re: Ballistics Results from Using Lapua Radar Data

What comes to G1 vs. true trajectory, with Lapua B408 Lock Base (250gr 338) using average BC of .570-.580 is usually good enough to give hits on bit larger papertarget between 100-1000meters.

Lapua advertised G1 BC is .662, but is valid only in faster velocity range. But thats way, way off in longer ranges.
G1 standard projectile is basically dia. 1,2" blunt-nose cannonshell. Drag graph simply cant be same.


Heres one earlier report about Quick Target Unlimited drops, compared with Lapua Magnum / Scenar:
http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=951143&page=1

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wwbrown</div><div class="ubbcode-body">, for ballistics calculations we may not need to rely on BC’s and directly use the drag curves offered by Lapua.
</div></div>

G7 has <span style="font-style: italic">basically</span> same problem than G1 -standard projectile is just closer to commonly used low drag modern BT:s. So, G7 gives drag grap match only with original standard projectile, just like G1 does.
Since G1 standard projectile was cannonshell, and G7 projectile .30 cal BT -bullet, G7 can give very accurate estimation of true trajectory.
Lapua Cd -values are based on bullet specific true trajectory measurements.

After all tests, I personally can not see any reason why not to use only free QTU with Lapua bullets.

 

[rmfield]

Re: Ballistics Results from Using Lapua Radar Data

"Out of curiosity, what are the std. conditions defined in Sierra Infinity? Are they the same std. conditions defined in JBM? I thought Sierra uses the ASM atmosphere model (59deg, 29.53inHg, 78%RH), and JBM uses ICAO (59deg, 29.92inHg, 0%RH)."

Brian, Sierra Infinity does indeed default to Std. Metro Conds., but of course you can tweak to give you ICAO.

 

[hexades1]

Re: Ballistics Results from Using Lapua Radar Data

If one has radar data then that is the most accurate data available for the regular guy. Second comes G7 and third G1.

Out to 1000 meters any of those suffice. When we go beyond 12-1300 meters G1 becomes quite inaccurate. Trajectory data is again the best but G7 is pretty close, depending a little on the specific bullet.

Unfortunately most civilian bullets do not have radar data available so we are stuck with either G1 or G7. Litz did test most of the relevant bullets for G7 values so I use those values in QTU.

 

[wadebrown]

Re: Ballistics Results from Using Lapua Radar Data

I agree that Bryan has done a very good job and given the shooting community a great resource. I looked at the comparison to see what the difference was between using Bryan's measured BC's and radar drag curves. The differences turned out to be so small that I do not see any loss to the shooting community by using Bryan's BC for the bullets we do not have radar data for.