Is there online ballistics software...

[Nukes]

... that would allow me to input specific come-ups at specified distances to generate a curve for calculating intermediate distance come-ups and a range card?

[Jon A]

The only program I know of that will do that sort of thing is EXBAL, which isn't available online I don't believe. With other programs you need to try and manually fit the curve by changing the velocity, BC of the bullet, etc. For online stuff I use JBM.

Again, the proper thing to do is to figure out why your observed come-ups differ from the program and fix it. Then the problem has taken care of itself. You not only can find your comeups for intermediate distances, but you can see what they'll be under different conditions--temp/altitude. You're prepared to actually make hits no matter where you are or what time of year it is.

Without doing this, even the most painstakingly, meticulously made best-fit curve is close to useless once the weather changes or you go shoot at a different range.

[Nukes]

[Drifter]

...the iPhone Shooter app corrected for temperature, but maybe only for the exterior ballistics, maybe not for increased pressure/MV. If the programs do not extrapolate higher MV from higher temperature, that may account for the disparity.

When I set up a load in Shooter (Android), MV Variation (fps per degree temp change) can be inputted, along with the Powder Temp and MV. I don't think this can be changed when using the results part of the app, as this data would need to be input via the load edit feature (or when the load is originally set up). Hope this makes sense...

Also, reference this list of reasons why actual results might not agree with ballistic predictions:

http://www.arcanamavens.com/LBSFiles/Shooting/Downloads/Programs/

[Nukes]

[mongoosesnipe]

I like the jbm online trajectory calculator

[BjornF16]

jbmballistics has the Litz G7 bc for the 108 Scenar but not the 123 Scenar (yet).

The 123 Scenar is likely going transonic at 1000 yards. Using a single bc for the entire profile will likely result in inconsistencies, particularly if it is a G1 bc.

Litz lists the following for 123 Scenar bc's in his book:

3000/M2.68 G7=.267 G1=.544
2500/M2.23 G7=.266 G1=.530
2000/M1.79 G7=.263 G1=.522
1500/M1.34 G7=.266 G1=.479

JBM Ballistics will allow you to override the default G1 bc for a "custom" G1 or G7 coefficient. If you choose the G7, then .265 is a good average.

I used the JBM Ballistic program for iPhone (Ballistic AE) and achieved a .25 MOA worst case difference in calculated vs actual between 400-700 yards (bolt action Grendel using 123 Scenar). YMMV

[Jon A]

[Nukes]

jbmballistics has the Litz G7 bc for the 108 Scenar but not the 123 Scenar (yet).

The 123 Scenar is likely going transonic at 1000 yards. Using a single bc for the entire profile will likely result in inconsistencies, particularly if it is a G1 bc.

Litz lists the following for 123 Scenar bc's in his book:

3000/M2.68 G7=.267 G1=.544
2500/M2.23 G7=.266 G1=.530
2000/M1.79 G7=.263 G1=.522
1500/M1.34 G7=.266 G1=.479

JBM Ballistics will allow you to override the default G1 bc for a "custom" G1 or G7 coefficient. If you choose the G7, then .265 is a good average.

I used the JBM Ballistic program for iPhone (Ballistic AE) and achieved a .25 MOA worst case difference in calculated vs actual between 400-700 yards (bolt action Grendel using 123 Scenar). YMMV

[Nukes]

Yeah, the velocity is probably the biggest wildcard here. The way Shooter adjusts is great for field use provided you've chronographed at different temps so you have some idea what to put in the box. Also don’t forget the distance to the chronograph...

Yes, that is project #1. We will chrono in the heat.

...Measuring scope clicks is a given—even quality scopes are commonly off 2-3% and when you do the math—that’s 3 clicks at 1000 yds right there without any other error....

Yes, project #2. We will run a CATS target this weekend. Too big a project for a work day.

...Wind will affect elevation—obviously tail and head winds, but people often forget about the vertical component caused by a crosswind—winds from the right tend to cause bullets to impact high. That’s if you’re shooting over nice, flat ground—across a coulee or canyon where actual updrifts/downdrifts are possible things can go out the window in a hurry. Really windy days are great for honing your skills, but they aren’t the best time to try and collect accurate data....

...It can be frustrating, but once you have things figured out you’re in much better shape for future challenges.

However, I would warn 1200 yds is pretty far for a Grendel. Strange things start to happen when the bullet gets close to transonic speeds effectively playing games with the bullet’s BC and you can’t really get good data for it. Lapua’s CD data (from Doppler Radar) is probably the best you can find, but even that may be inaccurate at such low speeds if the twist of your barrel is slightly different or any number of other small variables that don’t make much difference at closer ranges.

In short, even if you have your ducks in a row ballistically I feel that’s beyond the limit of what you can reasonably expect to predict with accuracy from a program even if all the inputs are correct. If you get the data to match at 500, 750 and 1000 I’d say you’re golden, and wouldn’t go changing things that would mess up those ranges due to a discrepancy at 1200.

Agreed. Hits on IPSC steel were easy at 1,000 yds., but clearly the precision was falling apart at 1200 yds. Our data confirmed that we were going transonic, so we didn't waste 6.5 Grendel ammo at the longer distances. We were curious how far out the Grendel could keep up with real XLR cartridges. For that little pill in an 8 pound package with an 8x scope, we were impressed that it didn't peter out until 1200 yds.

Mark Gordon at Short Action Customs did a superb job on that little rifle.

[Jon A]

Sounds like you're well on your way, let us know how things turn out.

A couple notes on BC's--for those using JBM they have Lapua's CD data loaded for Scenars which is Doppler radar derived and should be a tad more accurate than using constant G7. Also, when using Litz' data I try and pick the relevant velocity range to come up with an average--if launching in the 2500 fps range, I see no reason to include the 3000 fps value in the average--throwing that out will only drop the average to .265 with this bullet, but it makes a bigger difference with some other bullets (that don't have such a constant G7 BC).

Anyway, the difference between the CD data and .265 constant with this bullet is only about 2.9" at 1000 yds, less than one click, so we're starting to get into the minutia. That is a parameter I will change--very slightly--for fine tuning only in the end when all the other bigger problems are sorted out. That, along with velocity.

For fine tuning the shape of the curve in the end--if you are dead on at 300, 500, 800, etc, but a bit low or high at 1000, tune the BC a tiny bit. If you're little off at 500, a bit more off at 800, even more at 1000 but not dramatically so, then tune the velocity and leave the BC alone. Velocity error will be somewhat linear in magnitude with range. A small BC error will go from being tiny/unnoticeable in mid ranges to being significant at the very longest ranges--disproportionately affecting the longest ranges you shoot.

[Nukes]

[Nukes]

CATS target shows that the scope tracks just fine.