Range Report JBM vs Shooter

[tucansam]

Using the exact same data, and filling out the exact same fields, JBM and Shooter are giving me different results. I believe the fields that each has that the other does not are either irrelevant, or I left blank (or zero).

Which should be trusted more? I realize I need to shoot the rifle to get actual data, but I'm doing some load plotting to aid in bullet and scope selection.

Thanks.

 

[tucansam]

OK. So using JBM and Shooter, with Litz's G7 data, both are calculating that the round stays supersonic to 2000m (how in the world is this possible)... I'm working with a 2800fps MV to test. I've got the final output numbers to match a little better:

Numbers to 1km with 25mph wind from 270 degrees, 75 degrees ambient, 5000ft elev, std pressure, all other variable identical, shooter is not calculating coriolis, both are calculating spin drift. Basic output:

Shooter: Up 7.7 mils, left 3.3 mils, 1831fps, 1.45s tof
JBM: Up 7.8, left 2.7, 1887fps, 1.429s tof

I realize that these numbers are very close (except for wind), and that both programs use slightly different equations. But if I model the same in .338, and push it out to 1500m, the range of difference becomes larger. I'm tempted to just average both programs' output before I go to the range, but then part of the reason I want to use one or the other is for the ease of printing out range cards to take with me VS developing my own in Excel (I don't know any trig).

Still trying to figure out if its my error (my guess) or something else going on.

 

[EMorr]

Using my favorite load I cannot duplicate your problem, the most descrepency I can get the programs to produce is about 2 tenths of an inch at 1500 yards.

I do have to ask though, I have heard some people refer to Ballistic for ios as JBM, so are you using the JBM ballistics webpage or the Ballistic app, they both use the JBM engine but ballistic has different options for wind input, which could be contributing to your issues. Also ballistic and JBM will alter your entered MV and Shooter will not based to the distance to a chronograph, further compounding the problem.

Not sure if this will help, just some random thoughts I had.

 

[Drifter™]

The difference might be this feature on the Shooter app:

"Automatically populate Altitude, Temperature, Pressure, Humidity and Wind Speed by pulling data from the nearest weather station based off GPS location (Density Altitude may also be used instead of altitude/pressure/humidity input)."

Link to source: Shooter - Ballistics Calculator for iOS and Android

 

[BryanLitz]

I'm highly familiar with both JBM and Shooter. The two should give you equal (within roundoff error) answers given the same inputs. I suggest the following:
Enter the BC manually in case the number in the library is wrong/outdated
Pay careful attention to the air pressure (station vs. corrected) input
MV auto corrected for chrono distance as stated above
Check Coriolis option
For windage, this looks like the difference between spin drift on vs. off.

Please let us know what you find. Chances are it will be something others can learn from.

Thanks and good luck,
-Bryan

 

[chefcam864]

I'm highly familiar with both JBM and Shooter. The two should give you equal (within roundoff error) answers given the same inputs. I suggest the following:
Enter the BC manually in case the number in the library is wrong/outdated
Pay careful attention to the air pressure (station vs. corrected) input
MV auto corrected for chrono distance as stated above
Check Coriolis option
For windage, this looks like the difference between spin drift on vs. off.

Please let us know what you find. Chances are it will be something others can learn from.

Thanks and good luck,
-Bryan

I used shooter today to sight in at 300, 500, 600, 900, and 1,000 yards. It was .25 moa low at each distance. That's pretty close, I think. Anyways, I've run into weird numbers with shooter, using G7 BC too. For example, it told me that a 168 Hornady BTHP launched at 2536 fps will still be traveling 1639 fps at 1,000 yards. I know that can't be right. I pulled the bullet from the library, but it may have been a mistake on my part.

 

[XL Mammal]

Keep on eye on the Powder Temp "Enable" box. I've found that to be problematic if not used properly.

 

[chefcam864]

I'll have to check that out

 

[sinister]

Wow.

Ballistic trajectory arcs will be closer to calculate than wind holds.

I don't mean to sound likie a nay-sayer, but if you can nail wind correction to within a single quarter to 1/3 minute (~.1 mil) click for a first-round hit at 1500-2000 Meters you are a certified big-head brain and legitimate bad-ass.

Of the folks on this board I'd imagine Bryan's input, along with live on-site weather station feeds (Kestrel) will give you the closest estimates. I don't have a hand-held (phone, tablet, Kestrel, or notebook), so I rely on pre-calc'ed tables using JBM and weather off the internet.

Even with software-derived solutions wind over terrain is not homogenous over distance. I'm sure some day they'll devise an economical alternative to the M1A2 Abrams fire control system for rifles.

I understand shopping for data to compare scopes, barrels, and loads, but you'll never know for sure until you're on-site and squeezing the trigger.

 

[chefcam864]

Shooter was only .25moa off from what my actual 1000 yard elevation ended up being

 

[Drifter™]

Of the folks on this board I'd imagine Bryan's input... will give you the closest estimates.

Agreed. I wouldn't have bothered to post had I known that Mr. Litz was gonna weigh in. Kinda felt like I was telling people what it's like to walk on the moon without realizing that Neil Armstrong was standing behind me.

 

[woodland-ghost]

I have knights Armco bullet flight and shooter, they both give me the same info
Somewhere one of the two programs probably have diff data entered compared to the other

Today I sighted in my 338 at 100, ran it over the chrono and jumped straight to 760 yds, shooter/me was off .2 mill.
Put in the actual mills needed to calc MV and it gave me 2770 instead of the 2730 my chrono put out.
Moved back to 840 yds, dead on, and then back to 1180 yds, again dead on.

Idk what I would do without these programs lol but they def work. Thanks Litz!

But like what I've read befoe on these programs...crap in, crap out. It's definitely true.

 

[tucansam]

I appreciate the info from all. I still haven't nailed down exactly what I did wrong, but the point is it looks like *I* did wrong. I am now getting closer results when I take my time and WRITE DOWN my info first (novel idea right?) and then have careful notes to use for input on both programs. I am still learning what all of the variables mean, and how to supply accurate data for said variables. Most likely I was supplying what I thought was correct, but one calculator or the other was configured wrong, ie, I had a checkbox marked on one and didn't account for it on the other, etc.

As far as just getting out and shooting... Well that's the idea, after I use some dope charts to tell me if I want a scope with 5mils adjustment or 10mils based on the ranges I'd like to try. And the charts are also helping me decide on a couple of loads to try out using theoretical data compared to my reloading notes. Not to mention caliber selection of my next rifle. And the fact that one rifle was zero'd in the dead of winter, and its now 60 degrees hotter here. It was in doing these things that I happened to notice a difference in the output between both calculators, and figured I'd post to gain some knowledge about their use before I head to the range and spend more time fumbling with my phone trying to learn than I do behind the gun.

I find these programs are just as useful off the range as on it.

Again, thanks to all.

 

[sinister]

Best of luck, and keep us up to speed -- good input saves us the pain of new speed bumps!

 

[Joe L]

"man with two watches never is sure what time it is"

Joe

 

[2clicks]

Shooter app has been dead nutz on with my 260 GAP to 600 only variance I saw was with the sight height above bore option. As I shoot irons and scope off the same rifle. All other calibers have been within 1/4 moa most likely my error.