My son and I often chat about long range considerations and yesterday we talked about Brian Litz new book Applied Ballistics For Long-Range Shooting 2nd Edition (I have read his first book) and the fact that Brian is shaking up the Long Range shooting world with his plain speak on rifle bullets, rifles and twist rates but using physics to demonstrate by numbers the rationale for changes in the shooting world. It may be too much for a novice but hopefully some of you have the desire to shoot long range. It is also the remaining bullet energy and bullet stability at long range that is sufficient to make the shot count. In a hunting environment, many of us are not skilled marksman to make a clean kill on a deer at long ranges beyond 300 yards because we have few places to practice at those ranges and calibrate your scope to a particular bullet and load. But let us say that we do have a place and you have a long range rifle such as a 6mm or 7 mm or a .308 caliber rifle. The key here is what are we doing when the bullet arrives, paper punching or downing a deer or elk? It makes a significant difference in that the deer and elk require lots of energy delivered by the bullet to enter the animals vital area,provide hydro-static shock, mushroom and exit the animal.
As I have said in previous articles that as a guide you need around 1000 ft-lbs striking energy for deer and around 1500 ft-lbs for elk and some include that at these energies the bullet should meet a speed criteria of 2000 fps for a lead bullet to mushroom fully(I think that this speed varies with bullet material and construction but is still a good guide). In order to calculate striking energy at a given distance you must know the bullet diameter, the bullets ballistic coefficient either as a G1 projectile BC which most of today’s bullet manufacturers provide on the box or the G7 BC.
Chronograph your bullet speed: Then we must measure the bullet speed using a chronograph. I use an inexpensive Shooting Chrony F1 Green. (Cost $100) For long ranges beyond 300 yards the bullet must be shaped to reduce drag thus a pointed bullet is needed. Further that the shape of the tip, the o-give or curvature of the head and the body and the tail of the bullet are critical in maximizing the retained downrange energy. Another component is the twist rate of the rifle to shoot some of these bullets at heavier weights. For example the .243 Winchester needs a faster twist rate than say 1:10 to shoot bullets above 90 grains. Above 100 grains the data provided by Brian in his book Applied Ballistics as well as his other books and DVD’s on shooting that the Long Range enthusiast should purchase to develop the technical skills and know how. Ok so you go to the range and shoot your bullets through a chronograph. Lets take for example my .243 Winchester which shoots a 100 grain bullet through my Ruger American 1:10 twist at 2820 fps and is amazingly still stable. It has a G1 ballistic coefficient (BC) of .373.
Calculate your drop table: Using the website http://www.jbmballistics.com/ you can go to the ballistics page and click on trajectory. There you can enter all the specifications of your bullet, BC and speed, zero range, temperature, humidity, wind speed and angle and distances you wish to chart the bullet to and it’s incremental data points. I calculate that my 100 grain bullet when zeroed for 233 yards is going to shoot 2.7 inches high at 100 yards and drop to 3 inches low at around 273 yards which is my max point plank range. This is all based on accuracy of the data. Now you can shoot to verify the data by shooting at 2.7 inches high at 100 yards and then shoot at a range for 200 or 250 yards if possible to see that there is a match for the data in the output of the data table. At 150 yards you will be 2.9 inches high, at 200 yards you will still be high by 1.7 inches and at 250 yards you will be below the zero point by 1.1 inches. I do not have a capability to test shoot further than 200 yards so that data point of 1.7 inches high will be key to see and validate. This data validation will give you great confidence in the field when hunting.
Wind is a factor that can make or break your shot on long distance game. For example I can shoot out to 273 yards as MPBR – Max Point Blank Range but with a 10 mph wind at 90 degrees crosswind the bullet is off target by 7.4 inches. So you must account too for wind speed and direction. If the wind is blowing into your face, or from behind then the wind can often be discounted to a degree for its lateral effect on the placement of scope crosshairs. By experimenting with the ballistic software you can see the effects of wind on the bullet. Good Shooting!