Home Tutorial Video Manuals Support Pricing About Us Contact
 
 

Desktop Features

FFS Delta Software
A Brief Tutorial
How to Get the Most out of this Software

This software incorporates a set of tools for the shooter to wring the most out of his equipment and to maximize the chances of a cold-bore, first round hit on target. To use the tools requires a certain level of competence and effort. If the shooter either does not have the level of knowledge necessary to engage this software or does not want to expend the effort necessary to develop the data necessary to create useful and meaningful trajectory output, then he will not be able to get the most out of his software investment.

Preparing to Use this Program
Three Important Steps - Calibrate Scope , Determine MV, Calculate a BC

Calibrating the Scope - The only way a shooter knows how much his bullet actually drops over distance is by using the elevation turret of his scope to tell him how much elevation was required for the shot. What if the turret isn’t accurate? What if the click value of the scope isn’t what the manufacturer says it is? What if the click value is off by 4%, 7% or even 10%? For example, a Leupold Mk V, M3 is advertised to have a 1 MOA per click turret. A shooter who is shooting the .308 Win cartridge may find that it takes 42 clicks from a 100-yard zero to be on target at 1000 yards shooting M118LR ammunition and would therefore assume that for the conditions at hand, the bullet drops 42 MOA at 1000 yards and any computer program that forecasts a different theoretical result is simply wrong. After all, one doesn’t argue with reality.

If the shooter were to put on another scope on the same rifle, he would expect to dial in 42 MOA and be right on target. That may or may not be the result, however, because it is not necessarily the case that the turrets on the scopes are moving the reticle the same amount - on scope one, the turret says 42 MOA but in reality it may have moved the reticle only 40.7 MOA; on the second scope the turret says 42 MOA, but it may have moved the reticle 42.9 MOA. Just because the manufacturer says that a given turn of the turret moves the reticle a given amount on the target is NO assurance that it in fact does. The shooter needs to check. This is the essence of scope calibration.

The first thing any long range shooter must do is calibrate his scope to determine exactly how much the reticle moves with each click of the turret and NOT to take the manufacturers word for it. The program comes with a PDF file that prints out five sheets of 8½ X 11 paper, each with chart lines printed thereon. Assemble the five sheets in order on a cardboard backing of some sort and place the chart at 100 yards or meters. (If the file is not available, just take a long sheet of paper about 45 inches long, put a visible mark at the top and one at the bottom. Use the top mark as the starting point and move the reticle to the bottom mark.) Fix the rifle in a vise or with sandbags, dial the scope to zero, align the horizontal element of the reticle at the “0” (or top) line on the chart and then dial in 40 or so MOA and watch the reticle move down the chart. Keep track of the number of clicks of the turret and note the line number on the chart. Do this a few times to assure an accurate measurement. Now that the number of clicks has been recorded for a known distance of travel, double check the distance traveled on the chart by measuring the distance on the chart with a tape measure. Then use this data to compute the ACTUAL click value of the user’s scope. The program has a computation dialog box for this purpose and requires as inputs the actual and accurate range at which the measurements were taken, the number of clicks of the scope, and the corresponding distance the reticle moved on the chart or target. Once the user knows the actual click value of his scope, he can use this value 1) to compute the actual drop of the bullet at range; and, 2) to compute the exact turret setting for any firing solution computed by the software. This value is used in the Turret Profile so the program can accurately calculate a turret setting for any given drop.

In obtaining this data it is important that the shooter accurately measure the actual distance between the scope at its turret and the face of the target. Use either a good rangefinder (one that has an error factor of under a yard, hopefully in 10ths of a yard) or a tape measure. Errors in distance will have a definite effect on the calculations. You only have to do this once for each scope, so do it carefully.

While checking the distance the reticle is travelling, make sure the rifle is vertical and that the reticle is moving exactly vertically.  If the reticle is moving to one side or the other as the reticle moves down, the scope itself is creating a windage error.  This is a pernicious problem; it is, in fact, difficult to get a scope mounted exactly square to the bore.  (To get an understanding of the problem, go to http://www.scorehi.com/ and scroll down to the article "Precision Scope Mounting".  Work out a method to insure that the scope is properly mounted squarely on the rifle; you should see no horizontal movement of the reticle as it is dialed down 45 MOA. 

Obtaining Muzzle Velocity – Any ballistics program, this one included, must have the muzzle velocity of the bullet for each cartridge used by the shooter. But the velocity of a bullet measured 15 or so feet away from the muzzle, where the chronograph is located, is not the muzzle velocity. The program has a dialog box to help the user calculate what the actual bullet velocity at the muzzle given the measured velocity at the chronograph. Further, it is necessary that when the chronograph data is collected the shooter also notes the air temperature at the time. Why? Because when shooting the same cartridges later the temperature may not be the same which means that the powder temperature will not be the same which means that the muzzle velocity may not be the same. By noting the temperature that existed at the time the chronograph data was obtained, the shooter can input that data in a Bullet Profile and allow the program to correct the muzzle velocity for temperature. Therefore, with the actual muzzle velocity computed at a known powder temperature, the shooter can be assured that the proper muzzle velocity will be used by the program when computing a firing solution in the field.

Be sure to use a decent chronograph. Since chronographs are not self-calibrating, the user is taking a lot on faith that the chronograph is accurately measuring the bullet’s velocity. Use the highest quality of chronograph that is available and, if possible, get velocity data from more than one chronograph. Be sure that the data collected is accurate. The Delta III SD and the more advanced programs have a tool to check the chronograph and that is the "POI Method" tool.  More will be said about verifying the chronograph results below.

Computing a Ballistic Coefficient – Now that you’ve got a muzzle velocity from the  chronograph, take the chronograph and place it down range. How far? Far enough that the bullet will experience a meaningful reduction of velocity but not so far as to risk hitting the chronograph. Depending upon the size of the bullet path opening on the chronograph, you should be able to safely put bullets over the chronograph at 300 to 500 yards/meters. Fire a number of rounds at this new range and obtain an average downrange velocity for this bullet type.  The Delta III SD and above programs have a workspace to perform this calculation.  At this point, you have a calculated ballistic coefficient for the bullet that will be good for this bullet into the subsonic region using this program.

However, the work here is far from finished. As was mentioned, chronographs are not self-calibrating. The shooter has no idea if the chronograph is outputting data that is accurate or merely "close" or, for that matter, not even close. If the muzzle and down range velocities are off, the calculated BC for the bullet will be off as well although the error will be proportionately less. So, for example, if the velocities are high by 10%, the calculated BC will be high by approximately 5%. Therefore it is necessary that the user figure out if the chronograph is reporting accurate velocities and, if not, 1) determine the actual velocity for use in the bullet profile and 2) obtain an error factor to recompute the down range velocity for purposes of computing a more accurate ballistic coefficient.

Verifying Muzzle Velocity using the POI Method - Using the chronograph muzzle velocity and the calculated ballistic coefficient, set up a target at around 400, 500 or 600 yards/meters, adjust the scope for the range of choice and fire five (5) carefully aimed shots. Measure the point-of-impact distance above or below the point-of-aim, use the workspace in the program (Delta III SD and above; see "POI Method - Muzzle Velocity in the Field" in the manual) and compute the muzzle velocity as shown by the actual impact points on the target. Depending upon how well the user shoots and how small the resulting group is, this is an extremely accurate way to determine muzzle velocity. Once the actual muzzle velocity is known, first update the bullet profile with this known muzzle velocity. Then, use the original muzzle velocity obtained from the chronograph and divide by the POI Method muzzle velocity. This will give you an error factor. Use that error factor to modify the down range velocity obtained from the chronograph and that will give the actual down range velocity. Using these two corrected velocities, compute the ballistic coefficient again. (It is assumed here that whatever error existed when using the chronograph near the muzzle, that same error will be present at the down range target. It is important, therefore, that the two measurements be taken at near the same time and under the same conditions to maximize the chances that this is true.)

Using this newly calculated ballistic coefficient, run through the process again: if the turret solution remains unchanged, assume the same POI distance on the target and recalculate the muzzle velocity, get an error factor, using the error factor compute the down range velocity and using these two velocities calculate the BC for the bullet. It should be very close to the previous result. If the scope setting did change, then adjust the scope and fire five (5) more carefully aimed rounds at the target, measure the POI versus POA distance and recompute the muzzle velocity, then proceed with obtaining an error factor, apply the factor to the down range velocity and recompute the BC. At some point this iterative process will produce no meaningful change in velocity and BC at which point the user can be very sure that he has a correct muzzle velocity for that load/bullet/temperature and a BC that will produce optimum down range elevation and windage calculations well into the subsonic region.

Someone may well ask why it is necessary to go through all this work just to use the program. The answer is that it isn’t. But it must be understood that the program will assume the accuracy of all data that is input and based upon that data will provide a firing solution. If the input data is erroneous, the resulting firing solution will be erroneous. In order to discover the errors in the measuring devices that shooters depend upon, it is necessary to check them and to make allowances for their inaccuracies when detected. There really are no shortcuts in this regard.

Computing the DK - Most all ballistic programs will compute a trajectory based upon muzzle velocity, bullet configuration (i.e., the ballistic coefficient), and atmospheric conditions. This program uses the same data. BUT, this program also calibrates or customizes the trajectory to the cartridge/rifle/shooter. The manner in which a shooter manages his rifle, i.e., the interface between shooter and rifle, differs from shooter to shooter, rifle to rifle. This is one reason why two shooters who shoot the same rifle using the same ammunition can have bullet groups located at two different spots on the target. To have truly accurate trajectory computations, it is necessary to tailor the trajectory computation to the cartridge/rifle/shooter system and this program allows the user to do that.

The user must determine the actual bullet drop at sufficient range but where the bullet is still supersonic but at a point where the bullet has experienced significant drop. This range will differ depending upon the bullet in question but it is suggested that the user find a range where the bullet is moving between 1200 to 1400 fps. The following is an example of how to go about computing a DK. Let us suppose that a shooter is attempting to calibrate the trajectory for a 190 gr. Berger VLD which he uses in a 300 Win. Mag.. He chooses to measure the bullet’s drop at the 1000 yard range believing the bullet to be well above the speed of sound at that range. He uses the program to determine that under the conditions present at the range during this test, the bullet's velocity at 1000 yards is approximately 1435 fps. That is close enough. The shooter records the atmospheric data (air temperature, humidity and pressure) and takes three to five well-aimed shots. He records that his scope (which he has calibrated as described above) used 27.384 MOA to get the bullet on target with a 200-yard zero and that the program predicts a 27.4 MOA bullet drop. Upon studying the targets, he notes that the group is actually 6 inches below point of aim, so in actuality the bullet drop was 27.957 MOA (6 inches equals 0.573 MOA. Add 0.573 to the actual MOA correction dialed by the scope.) Using this data, the shooter computes that bullet’s DK by inputting the data in the DK computation dialog form supplied in the program. For this bullet under the existing atmospheric conditions, the program computes a DK of 0.498. When the shooter uses the same atmospheric data, muzzle velocity, ballistic coefficient and DK to compute the trajectory for that bullet, the program correctly predicts a bullet drop of 28 MOA. The trajectory has been calibrated for that bullet/rifle/shooter system and as the weather conditions change or muzzle velocity changes, the program will still accurately compute trajectories for that system as long as the system does not change. This means that if the shooter changes the manner in which he assembles his cartridges, changes the powder, changes his firing position, he needs to check the impact points to make sure the DK is still valid. It is a good idea to compute a DK for each cartridge and rifle combination the shooter owns.

The default DK of 0.5 is a good place to start and many have found that it suffices for all but the most demanding work. If extreme accuracy at extreme ranges is required, however, the user should take the time to compute a custom DK.  CAVEAT: Do NOT, DO NOT, DO NOT change the DK from its default value until 1) the scope has been calibrated, 2) the scope has been zeroed, 3) a muzzle velocity has been obtained and verified via the POI method, and 4) a ballistic coefficient has been calculated. If the shooter tries to use DK to get agreement between the actual and calculated trajectories using erroneous muzzle velocities and ballistic coefficients, the program will produce a distorted, inaccurate trajectory. The DK was not intended for this purpose and will yield completely unusable data. Don’t do it.