Long Range Shooting Essentials
Basic Essentials Of Long Range Target Shooting - Part 2.
In Part 1 we gathered together some basic data in the form of the riflescope adjustment, bullet velocity, bullet specification and we used a representation of the target called a plot sheet. This info when used with Berger Bullets ballistic software enabled the new shooter to find the centre of a target at any range distance. So far so good!
As long as we are shooting the same ammo at the same velocity with the same sighting system, the drop chart will be consistent for all ranges. However if you change one of these components then that drop chart wont be accurate anymore. So if you decide to use a different bullet or powder charge or fit a new set of scope rings, you need to repeat part 1 all over again to establish a new drop chart. Whenever you make a significant change to your target ammo or riflescope you need to re-zero the rifle and record the bullet velocity. Its a repetitious process that must be followed if you want to be on target at all ranges.
Using Ballistics To Gain An Advantage
Bryan Litz in his book "Applied Ballistics For Long Range Shooting" makes it pretty clear that wind deflection has a greater bearing on accuracy than bullet drop. Bullet drop over distance does not present as much of a problem as the range distances are known and precise adjustment can be made. Wind is largely unknown and guesstimated in competitions, so less bullet drift in wind is a definite advantage.
It comes down to a projectile's BC (ballistic coefficient) and the higher the BC the better. High BC bullets resist the effects of drag better than low BC bullets. If we concentrate on the "Drift" column when using the data generated by ballistic software then we are looking at the most significant ballistic data.
Berger's 7mm, 180gr VLD & Hybrid, High BC Bullets
Bullet drift is the most significant element when comparing ballistic charts for loads you are developing and testing. When competing you need to know how far your bullet will be deflected in wind changes in order to hold the centre of the target. In competitions you need to be as familiar with bullet drift as possible and to know what the adjustment is in MOA for the wind speed.
Another crucial element for a ballistic chart is to check to see that the velocity of the bullet is supersonic at the longest range you will be shooting on. The bullet's BC is velocity dependant and the data is generally not reliable for bullets under 1200fps. The Excel spreadsheet shown below is what I use to compare loads and calibres of interest when assessing the merits of one over another.
The Berger Bullets software presents data in a uniform way but by using Excel with some custom BfX ballistic functions, data can be displayed exactly how you want. These BfX functions are available for download and for use by those that want to create and use a custom chart to display their data.
The Ballistic Data Displayed On Excel
If using the Berger Bullets ballistic software to compare or to simulate loads you are developing, then you will need to print off quite a few charts and compare them side by side. When using a custom Excel spreadsheet you can have the results displayed side by side on a single sheet of paper. In Part 3 I will look more closely at the use of custom spreadsheets to evaluate different loads and outcomes. Read this article for more information on Robert Meijer's BfX Excel functions.
What Do The Calculated Results Indicate?
The results you will get when you run the ballistic software with different loads, projectiles and calibres will indicate the following...
The projectiles with the highest BC will have the least bullet drop and drift deflection displayed on the chart when compared to lower BC projectiles fired at the same velocity.
I consider the single most important element to be choosing the projectile to use in competition!
Why is this the case when there are so many other variables? The answer is simply that if your shooting a bullet with a higher BC than the shooter next to you and all other things are equal. Then your bullet is going to be less affected by wind and inevitably score higher when the wind blows.
When looking at manufacturer's bullet charts you will notice that in each calibre group, the projectiles with the highest BC will be amongst the heaviest bullets available for the calibre. If you want high BC bullets then you will be shooting heavy for calibre bullets. So now we need our ballistic charts to provide an indication of what is the best calibre to use with high BC bullets.
In F-Standard the calibre, (223R & 308W) and bullet are restricted, so its an easy task to compare projectiles and velocities. By checking manufacturer's bullet charts you quickly come to the conclusion that the 308W shooting HBC projectiles is by a small margin the best choice. The higher BC bullet and velocity for the 308W give it the edge.
Note: High BC bullets, particularly the VLD variety can be difficult to group consistently. Look at the photo of the Berger 180gr VLD and the 180gr Hybrid and notice that the nose on the Hybrid appears a little more rounded. The Hybrid is an attempt by Berger Bullets to have the high BC advantage of the secant ogive VLD with the easy to chamber ability of a tangental ogive. Basically a high BC bullet that is easy to set up to give tight groups.
It now comes down to picking a case and calibre that will launch your high BC bullet with sufficient velocity to be accurate and remain supersonic for the range distance required. What else needs to be considered in regard to ballistics to help sort out a suitable choice?
Continued in Part 3.
Note: If you want to run BfX functions you need to download and install Robert Meijer's Excel Add-in using the program provided here: Add-in BfX Functions
Ian Pavy safclass.com.au