Calculating range adjustment for ranges you have not shot?

[Gone Ballistic]

The point is, regardless of the speed your chronograph shows, once you see where the bullet hits on paper, you can adjust your speed on your ballistics chart to offset the impact setting on the chart. So this changes your Ballistic chart setting of your scope to adjust the impact of the bullet.

 

[Gone Ballistic]

Good question. So generally if a dial in is not matching the solution then clearly something is not correct in the ballistic inputs.

If youR dial to is 10 to be on target but the solution is 10.5, I'd take off .5 for the other ranges and send it. If this compensation is off or not correct then it's usually one of these: scope height, scope tracking, incorrect atmospheric data, g7 vs g1 numbers are reversed, parallax. For these shorter ranges FPS and bc will not give much error unless way off. I highly doubt you are way off.

It is more effective to adjust your bullet speed in your Ballistic chart. I found shooting at 600 yard and 900 yard targets will not correct impact by adding or subtracting an MOA setting and carry throughout the yardage spectrum. You must adjust your ballistics charts muzzle speed to get proper impact at different yardage.

 

[T3ninja]

Not sure if it has been mentioned BUT.... check your scope to be certain your click values are correct. This might get long winded here, but I'll try it. Confirm your 100 yard zero.

Then shoot @100 yards using your estimated 400, 500, and 600 yard "dope" and measure up to your groups from your aiming point. Make sure your scope is tracking exactly like it should, so when you actually shoot those distances, you know the scope is true. If it checks out, Now, go shoot your 600 yard target. If you're on @600 you know you'll be on at 4-500.
You could even do this @300. Shooting @300 yards, dial in your 400-500 yard "dope" shoot a group and make sure it's the correct height above your 300 yard aiming point.

If you're off @600 like you're concerned about, then triple check your data input on the app, maybe cross reference a couple different ones. Then adjust your MV accordingly.


I know you have a magneto, as do I. But sometimes it is off albeit not much. So, I'd adjust the MV to fit where the bullet impacts.

 

[Pro2A]

All,

my back yard range goes to about 300 yards however o have one spot where I can shoot 600 yards now. This is ONLY 600 yards due to obstructions and rolling hills. I have used jbm ballistics to calculate estimates for blank range but never for actual dialing in. So my question is let's say you worked up a load andthe ballistics program says dial up 10moa for 600 yards but you find out you actually need to dial up 10.5 or 9.5 or some other number. How can you take that info and back calculate for 500 and 400 yards etc?

First, you need to understand why the deviation. Cranking an adjustment into the system often reults in chasing one's tail in circles. There are soooo many varibles that might cause the observed discrepancy. What are the ES and SD for your rounds? How accurate are you measuring muzzle velocities? Ammo variations are a big factor in bullet impact performance. What scope are you running? Have you run a tall target test to confirm scope tracking accuracy? A budget scope like a Tasco won't track like a high level NF, Leupold, S&B, etc. There are even variables between all scopes. One must confirm their own specific scope performance. There are threads that cover how to perform the tall target test. Inaccurate scope tracking can be adjusted in your ballistics program as a multiplier. Better to adjust tracking inaccuracies rather than adjusting bullet velocity to fit the bullet flight. Always believe the bullet....it never lies. But, falsifying the bullet speed also falsifies the bullet flight. BCs, the bullet's ability to retain velocity, vary with velocity. Manufacturer's published BCs are commonly bias for Marketing purposes tending to be selected for highest BCs at higher velocity. Some manufacturers provide banded BCs with more accurate BCs for velocity ranges. I am not familiar with your ballistics program. Don't know if JBM accepts banded BCs. I use Applied Ballistics and Hornady 4DOF programs which offer Custom Drag Curves of the specific bullets. These are actual ballistic curves rather than a comparison to a theoretical projectile performance.. Also, consider scope mounting cant (rotated in mount) and rifle cant (lean right or left). Both modify dialed come ups (on the low side and to the side of cant)....scope cant is constant variable; rifle cant varies with each sighting. Also, are your yardages accurate? Ranging as 600 yards when actual range is 580 or 620....only 3.3% error... can affect results.....even 1% is a deviation input. You mention rolling hills. Topography, obstructions, etc can enter into the bullet flight. Wind is the most elusive variable, complicated by terrain. There is also wind direction, bullet jump, and Coriolis effect....all lesser importance at 600 yards...but, small inputs are additive and variable. And, don't forget the weakest link in the chain....we the shooter. How precise are you as a shooter? We all start somewhere, and hopefully improve from there. All these variables are additive. Even if very infinitesimal by themselves, in summary they can be very consequential and even more frustrating and elusive.....vary with each shot. That's a large part of becoming a shooter rather than a trigger puller....conquering the system. As an example. Bryan Litz Applied Ballistics guru drilled into the the development team for the latest SOCCOM sniper rifle system the Barrett MK22 that testing the rifle at long range was useless due to these additive effects. After all, the rifle only launches the bullet. Once it exits the barrel, the rifle is out of the equation, and the bullet flight characteristics and all the external variables take over. The team tested and verified the rifle at 100yds where the rifle could be isolated most effectively from non-rifle specific inputs. Outside the end of the barrel and certainly beyond 100yds, the other variables entered into the equation obscuring the specific rifle parameters. Good luck in ascending the learning curve. It can be a slippery slope and quite challenging, but very satisfying....and addictive.

 

[Pro2A]

This is what I was looking for. Thank you. I do have a question about scope height. Do you measure from bore centerline to scope bell center?

Bore centerline (where the bullet travels) to optic centerline (where you sight). It is an offset dimension.

 

[UplandFreak]

All,

my back yard range goes to about 300 yards however o have one spot where I can shoot 600 yards now. This is ONLY 600 yards due to obstructions and rolling hills. I have used jbm ballistics to calculate estimates for blank range but never for actual dialing in. So my question is let's say you worked up a load andthe ballistics program says dial up 10moa for 600 yards but you find out you actually need to dial up 10.5 or 9.5 or some other number. How can you take that info and back calculate for 500 and 400 yards etc?

Could be scope error as well. Some ballistic programs allow you to compensate for that since almost all scopes has some amount of adjustment error.

 

[Rooks]

Take the time to get ALL of the environmental data in the app right on. If you have cross referenced The MV with reliable devices then you're probably not going to have an issue, as long as you don't read into what you're seeing. Know that a combination of small changes can look like a problem when it's not. Something as simple as the rear bag not being crushed exactly the same as when the rifle was zeroed can easily be represented as a .5moa shift in POI, especially at 600yds. Faulty velocity readings or misrepresented BC are the least likely culprits.

 

[TBell]

All,

my back yard range goes to about 300 yards however o have one spot where I can shoot 600 yards now. This is ONLY 600 yards due to obstructions and rolling hills. I have used jbm ballistics to calculate estimates for blank range but never for actual dialing in. So my question is let's say you worked up a load andthe ballistics program says dial up 10moa for 600 yards but you find out you actually need to dial up 10.5 or 9.5 or some other number. How can you take that info and back calculate for 500 and 400 yards etc?

Ballistic AE has a feature that you insert the difference + 6" o maybe -10" and it will automatically change the velocity to fit that Scenario

 

[Canhunter35]

I feel this is a great thread showing an example of until you've chased your tail with a bad zero, or been forced to perform a tall target test checking your level and measuring ur scope tracking, until you've disproved a chrony by the targets repeatedly, there's just a whole a host of things to experience before tweaking bc imo

 

[Andrew Cowling]

I had simular issues. I was told a distance was 300m. With the velocity I had over the chrony did mot match my drop at that distance and fidfling with the velocity to match the drop stuffed up the dope from the app at longer ranges. True distance was 265m. Once the CORRECT distance was entered onto the app the drop match perfectly with the muzzle velocity. The app was also perfect at 897m
Make sure the range is correctly identified. I use Strelok pro.

 

[Stiltsville]

Simple solution. I have found there is a factory cartridge that will match up with almost anything.

If not, you can enter your own unique data.

Unless you're shooting crows, an inch or 2 is immaterial.

 

[milo-2]

So you're willing to bet your single measuring device is more accurate that the manufacturers stated BC? Interesting approach.

I'd just adjust the velocity. Or try both and see what gets you closest at your 300 and in targets. I'm betting one will have a measurable improvement over the other.

The general consensus seems to be to true your muzzle velocity to 600 yards to match your drops, adjust the BC after.
Some bullets will match your app, some never will. Some bullets BC drops off after so far, others seem to grow wings and fly better than predicted.
Berger hybrids are notorious for flying better after so far down the range, 6mm 110 Sierra also. In my experience, Hornady bullets drop off in BC, though I can't or don't have the time to prove it, I think for dopes to match up, that bullet needs to exit the muzzle at a certain velocity range. Go too fast, issues, go slower, issues.

 

[Capt RB]

First, do a tall target test with your rifle scope load combination. This will show you what exactly your turret is correcting to. Here are calibrated targets there are others but these work well.

Blog-Box to Bench Precision

www.boxtobenchprecision.com

You have velocity and you have a stated BC. What you don't have is tested form factor. Twist rate the way the lead is cut etc can effect the form factor by excessive coning angle causing a different bc due to more or less drag. If you use a Hornady bullet I'd highly suggest the hornady ballistics solver they have the bullet in their library along with many other brands. It allows you to tweak the form factor that trues up your solution faster.
It is when you have to start changing the bc due to velocity loss at great distance that you will have the major issues. There are not many bullets being used that you cannot find the real bc for today. Many have shot what you plan to shoot if there were real issues you would be able to easily find the necessary information to correct those discrepancies

 

[BallisticsGuy]

Depends on where the error comes from. Sometimes it's real BC versus advertised BC, sometimes it's scope click values, sometimes it's a product of imprecise inputs and sometimes it's just the little differences between how different calculators implement the math. Sometimes, it's even a hodge podge of each of those. Step 1, eliminate the variables that you can so you can discover the real source of the error. Then correct that error. I recommend most people to start with scope click values since those are subject to variance from unit to unit within a brand-model line.