G1 or G7 data for 123 gr A-Max

[jcampbellsmith]

I'm a bit confused. I've been shooting today with my 260 Rem at 400 yds using 123 gr A-Max. I've got a velocity of 2881 fps. Should I use G1 data in the App or G7 data in the App?

Thanks

JCS

 

[CJ6]

Which is closer to your actual drops?

 

[dcali]

Almost always, the answer is G7 for this type of bullet. G1 is better for bullet that have wide, flat noses and shallow boat tails. You won't see a difference between the two until you hit 600 yards or so, and it won't be significant until 1000 or thereabouts.

 

[jcampbellsmith]

Which is closer to your actual drops?

Roger

Thanks, that's a very good question. I've checked this evening and can summarise as follows:

1. In the field I applied elevation of 7 MOA
2. Later using App with G1 gives 6.2 MOA.
3. Later using App with G7 gives 5.3 MOA. This is the one that really doesn't make sense at all.
4. Today using on-line calculator both G1 and G7 give 6.3 MOA - approximated with 123 gr SST.
5. Today reviewing impact of 8 rounds implies 6.75 MOA elevation required.

Any thoughts on what I'm doing wrong here? All points make sense to me, apart from point 3. - the G7 Applied Ballistics App calculation which seems to be mince. Also approach 3 is what I would normally try and do, which makes it doubly frustrating.

Additional points for clarification. Speed measured using a Magneto Speed. A new Kahles 6-24 x 56 scope and it hasn't been checked using a tall target or box test yet.

Regards

JCS

 

[dcali]

If the G7 is off that far from the G1 at 400 yards, something is wrong. Either you mistyped another input, the bullet library has a typo, or there is some sort of software bug.

 

[jcampbellsmith]

If the G7 is off that far from the G1 at 400 yards, something is wrong. Either you mistyped another input, the bullet library has a typo, or there is some sort of software bug.

Thanks, prompted by your comments, I ran the 123 gr SST with G7 in the App, this gives me an elevation of 6.3, which matches the on-line app and my expectations.

I think the 123 gr A-Max data for G7 in the app is not correct. I've selected a G7 drag, but the data is showing a G1 BC. I've checked Bryan's book, but this bullet isn't listed.

Best regards

JCS

 

[jcampbellsmith]

Bryan

Is it possible to get the 123 gr A-Max G7 data and for me to manually add it in?

Thanks

JCS

 

[dcali]

Looks like someone fat-fingered the library data. It happens. Did you check the G1 BC? Maybe they got transposed.

 

[alf]

[quote author=jcampbellsmithlink=topic=3872429.msg36569121#msg36569121 date=1430157424]
5. Today reviewing impact of 8 rounds implies 6.75 MOA elevation required.[/quote]

So click your scope to match POI, dial down 6.75 MOA, set your zero, and call it a day.

 

[jcampbellsmith]

[quote author=jcampbellsmithlink=topic=3872429.msg36569121#msg36569121 date=1430157424]
5. Today reviewing impact of 8 rounds implies 6.75 MOA elevation required.

So click your scope to match POI, dial down 6.75 MOA, set your zero, and call it a day.
[/quote]

Alf.

I don't follow that at all. Why would I change my zero? The zero on the scope had already been set on previous outings and confirmed on this outing. Secondly, your suggestion does nothing to address the calculation inconsistencies between the App and the online calculator.

Regards

JCS

 

[CJ6]

An old fox hunter I know always said ....Put lead downrange and figure it out for yourself , I'm not tellen you nuttin (his words to me). So I've always shot to make my cards even after Programs n Apps came about. I use the programs for "rough-what if" figures but I always shoot it.

 

[Bryan Litz Ballistics]

When you toggle between G1 and G7, you also have to change the numeric value of the BC. For example, suppose you input a BC of .510, select G1 and calculate a trajectory. Now you go back and toggle to G7 without changing the .510 number and re-calculate the trajectory. This will give you incorrect data. The G7 BC of a bullet is lower than the G1 value (roughly half). So when you toggle between G1 and G7, you also have to input the correct BC number accordingly.

I've not yet tested the 6.5mm 123 Amax, but it's going on the list.

-Bryan

 

[jcampbellsmith]

When you toggle between G1 and G7, you also have to change the numeric value of the BC. For example, suppose you input a BC of .510, select G1 and calculate a trajectory. Now you go back and toggle to G7 without changing the .510 number and re-calculate the trajectory. This will give you incorrect data. The G7 BC of a bullet is lower than the G1 value (roughly half). So when you toggle between G1 and G7, you also have to input the correct BC number accordingly.

I've not yet tested the 6.5mm 123 Amax, but it's going on the list.

-Bryan

Bryan

Thanks, I just generated the screen shot above by adding a new bullet and selecting the G7 option. I didn't edit any of the fields.

What G7 value should I use for the 123 gr A-Max?

Best regards

JCS

 

[alf]

[quote author=jcampbellsmithlink=topic=3872429.msg36569121#msg36569121 date=1430157424]
5. Today reviewing impact of 8 rounds implies 6.75 MOA elevation required.

So click your scope to match POI, dial down 6.75 MOA, set your zero, and call it a day.

I don't follow that at all. Why would I change my zero? The zero on the scope had already been set on previous outings and confirmed on this outing. Secondly, your suggestion does nothing to address the calculation inconsistencies between the App and the online calculator.[/quote]

Are all your imputs correct? Sight height, elevation, temp, etc? What's the Magneto Speed's accuracy? Was your 400yd group an 8 shot? So your saying you have a .45 MOA discrepancy from the center of the group? You're fretting over a click or two at 400.

Run your data through JBM and see if they jive. Take it to 600 or a 1000, where it matters more, and see where you're at.

 

[dcali]

[quote author=jcampbellsmithlink=topic=3872429.msg36569121#msg36569121 date=1430157424]
5. Today reviewing impact of 8 rounds implies 6.75 MOA elevation required.

So click your scope to match POI, dial down 6.75 MOA, set your zero, and call it a day.

I don't follow that at all. Why would I change my zero? The zero on the scope had already been set on previous outings and confirmed on this outing. Secondly, your suggestion does nothing to address the calculation inconsistencies between the App and the online calculator.

Are all your imputs correct? Sight height, elevation, temp, etc? What's the Magneto Speed's accuracy? Was your 400yd group an 8 shot? So your saying you have a .45 MOA discrepancy from the center of the group? You're fretting over a click or two at 400.

Run your data through JBM and see if they jive. Take it to 600 or a 1000, where it matters more, and see where you're at.
[/quote]

What he's saying is that the wrong BC is being used, resulting in a 1 MOA error in the calculation at 400. This is fixed by using the right BC. I don't own the Applied Ballistics app, so I don't know why it's doing that (could just be user confusion, or it could be a subtle bug/user interface issue), but the answer is not "shoot and see what happens". It's "use the right BC". That way, the calculator will do what it's supposed to do and predict trajectories at all ranges, not just the ones you can test. Given that Bryan said he doesn't have data for that bullet yet, I would go with the Hornady supplied G1 and forget about G7 for now.

 

[Bryan Litz Ballistics]

^ this.

 

[alf]

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

 

[Acyr]

Why couldn't you tweak a G7 BC (start at ~.260) to match the known POI? If all other inputs are accurate? Reverse engineer it.

 

[boltfluter]

Jc,

I have shot the 123 A-max quite a bit in my 6.5 - 47 and the G1 bc has been spot on to at least 900 yds. Hope this helps. ;D

Regards, Paul

www.boltfluting.com

 

[dcali]

Why couldn't you tweak a G7 BC (start at ~.260) to match the known POI? If all other inputs are accurate? Reverse engineer it.

You can, but you have to have very accurate knowledge of the other inputs or you risk tweaking erroneously. It's safer to use a known good G1 value. Out to 600-700 yards, there just isn't much difference.