Need Help with Ballistics

[archp625]

I loaded up some rounds and went out this evening to shoot some groups and work on my dope chart.

My group at 1000 is excellent. But I am literally 2 MOA low at 20"



I am using the Hornady App and after punching in my info it told me to dial 24 MOA.

I am shooting a CA Ridgeline with 1:8 twist in 6.5 PRC.

Im using 147 grain ELD-M with an average of 2936 FPS, SD 5, and ES 11.

Scope height is 1.925"

Temperature was 66 F, 33% RH and 29.84 inHg. Shooting at 840 ft.

What are your apps telling you to dial?

Also what is the best app that you can recommend me?

 

[coues craze]

What is your zero range and what direction are you shooting (north, east, south, west)

 

[archp625]

What is your zero range and what direction are you shooting (north, east, south, west)

Zero at 100. Shooting West

 

[coues craze]

I’m running StrelokPro and mine says about the same thing yours is spitting out, but you could have a minute or so of Coriolis effect. Give this a look but you may already be familiar with it just thought I’d throw it out there.

Precision Long Range Shooting and the Coriolis Effect

This is another element that a long distance shooter has to consider along with wind, rain, snow, distance and elevation to make an accurate shot.

americanshootingjournal.com

 

[archp625]

I’m running StrelokPro and mine says about the same thing yours is spitting out, but you could have a minute or so of Coriolis effect. Give this a look but you may already be familiar with it just thought I’d throw it out there.

Precision Long Range Shooting and the Coriolis Effect

This is another element that a long distance shooter has to consider along with wind, rain, snow, distance and elevation to make an accurate shot.

americanshootingjournal.com

This is good. I didn’t know this was a thing to be honest.

I zeroed my gun at 100 shooting to the west as well.

Have you ever had to adjust your dope on real data? To me I need to dial to 26 MOA.

whwn you do this how do you factory that when going up in altitude. Zero at 1000 hunt at 5000. Would you take what the app tells you at 5000 then add 2 MOA.

 

[coues craze]

This is good. I didn’t know this was a thing to be honest.

I zeroed my gun at 100 shooting to the west as well.

Have you ever had to adjust your dope on real data? To me I need to dial to 26 MOA.

whwn you do this how do you factory that when going up in altitude. Zero at 1000 hunt at 5000. Would you take what the app tells you at 5000 then add 2 MOA.

I’ll try to simplify and answer your question as best I can. Once I’ve verified my drop data you can adjust your curve based on velocity and ballistic coefficient. Both of which may need to be tweaked a little to get your curve lined up with the data points you verified in the field. Once you’ve got that trued up you just put in your altitude for your shot and the ballistic calculator will compensate for the correction.

 

[archp625]

I’ll try to simplify and answer your question as best I can. Once I’ve verified my drop data you can adjust your curve based on velocity and ballistic coefficient. Both of which may need to be tweaked a little to get your curve lined up with the data points you verified in the field. Once you’ve got that trued up you just put in your altitude for your shot and the ballistic calculator will compensate for the correction.

No that totally makes sense. I appreciate the help. I use a magnetospeed so I’m confident in my velocity. So I probably should tweak BC. Thanks a million.

 

[archp625]

What are you using for a BC now?

.351 G7. It looks like if I use .300 G7 it’s more in line with actual.

 

[dirtytough]

Are you positive your scope is dialing properly?

 

[archp625]

Yes, have tested it and it’s level. If it helps any it’s a Nightforce.

 

[BRTreedogs]

I would true your data by dialing until it is hitting where you want,
Then adjusting sight height, velocity and bc until it matches your actual dial.

Edit, 20 moa is pretty far off though.

 

[Terrapin]

Pretty far off... if anything the numbers on my ap went the other direction.

I would check that my scope was moving 26.175 inches at 100 yards when I moved my scope 25 MOA.

Were you shooting across a canyon? We get updrafts and downdrafts out here. Only take 4 mph at 90 degrees to get 2 moa.


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[BRTreedogs]

20 Moa is pretty far off.
Have you verified at a closer distance?
You're sight height seems awful low for a carbon barrel rifle and a 50mm scope.
You're measuring center of bore to center of scope?

 

[archp625]

20 Moa is pretty far off.
Have you verified at a closer distance?
You're sight height seems awful low for a carbon barrel rifle and a 50mm scope.
You're measuring center of bore to center of scope?

Its 2 MOA off at 1000 not 20 MOA. Its's 20 inches.

 

[archp625]

I think I am going to go back today and make sure scope is still tracking correct and re confirm my velocity. I did see a speed up on my barrel but I have 251 down the tube now so it should be stable.

Thanks guys.

 

[BRTreedogs]

Ohh 2 moa is nothing to be off at 1000 the 1st time.
Just true your ballistics up.

 

[archp625]

I did some testing and confirming today. Here are my numbers:

2934
2931
2931
2942
2947

Avg= 2937; SD= 7; ES= 16

My speed has been consistent for three different days.

Turret Elevation test

Dialed Actual POI Expected Actual Correction
10 10.25 10.47 2% low
20 20.50 20.94 2% low
30 32.00 31.41 2% high

What adjustment would you make on your ballistic app?

 

[archp625]

That data set is relatively small and quite skewed, which means that the SD is likely incorrect and the ES is unknown (from a statistical standpoint). For small data sets, you should use the median instead of the average. That said, I've trued guns out to beyond 1,000 yards without ever shooting them over a chrono, so a small data set isn't the end of the world at this point. You could probably just start with the median MV as your "try dope" and tweak it at ~ 700 yards to real world.

How did you check your scope? The three primary items that you should check are tracking, return to zero, and zero retention. Tracking & return to zero should be a static test, and zero retention should be looked at under live fire. In an ideal world your scope should track 100%. But if you scope is consistently 98%, that error can get "true'd" out of the system by tweaking MV & BC - again, not ideal but it can work. If your scope is not consistent at 98% (i.e. it suddenly becomes 102%), I would send it back.

As far as what you should put into your calculator, you need to get actual drops at various ranges and then true your solver to real world. Again, typical practice is to adjust MV to meet real world results at ~700 yards, and then true BC at the furthest available distance. Then double check solutions at 100 yard intervals.

Excellent advice. I'm just so new to all of this. Prior to this 300 yards to me was a far shot. I don't plan on taking an animal out to 1000 yards. Its more of a for fun to see what I can do. To me 500 yards would be a max but I would try to get a lot closer to the animal.

 

[Tumbleweed]

You mentioned you are using the Hornady app. I have used 4DOF quite a bit too. There is a function called "Axial Form Factor" that will allow you to tweak the custom drag model for your Hornady bullet. It allows you to fudge your program output either up or down to correct for real world point of impact from your specific rifle.
It wont allow for a huge amount, but might just get you enough. Hornady has a great video tutorial on how to zero rifle and set up this function immediately after


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[archp625]

Alright guys, went out this morning at shot a few more rounds to verify some drops.

Shooting a CA Ridgeline 6.5 PRC 1:8 twist barrel. All my groups are .5 MOA out to 500 then go to 1 MOA at 750 and 1000 yards.

Shooting 147 grain ELD-M at 2937 fps.

55 F; Humidity 72%; Pressure 30.17 and 849 ft

I made sure my zero was zero.

300 yards dialed 3.25 shot three shot group, needed to come up .25 MOA, three shot group verified 3.5 MOA

500 yards dialed 8.00, shot three shot group, needed to come up 1 MOA, three shot group verified 9.0 MOA

750 yards dialed 15.25, shot three shot group, needed to come up 1.75 MOA, three shot group verified.

1000 yards dialed 26.00, shot three shot group, needed to come up 2.00 MOA, three shot group verified.

Whats odd to me is to get this ballistic calculators to work I need a BC of .545 instead of .691. Am I doing something wrong or should i roll with it and see if I can reproduce results another day.