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Long Range Hunting & Shooting
Calculating range adjustment for ranges you have not shot?
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<blockquote data-quote="Pro2A" data-source="post: 1922067" data-attributes="member: 17889"><p>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.</p></blockquote><p></p>
[QUOTE="Pro2A, post: 1922067, member: 17889"] 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. [/QUOTE]
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Calculating range adjustment for ranges you have not shot?
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