(Continued from Part 2.)
Understanding Ballistic Coefficients
As a rule of thumb, projectiles with a ballistic coefficient (BC) of 0.400 or less and velocities of less than 2,750 fps (such as 77 grain .223 bullets out of 20″ AR barrel) will have a much more difficult time striking targets past 600 yards when compared to projectiles with greater ballistic coefficients and the same or higher velocities. The larger diameter projectiles with heavy for caliber bullets used in other cartridges beginning with 6mm ARC, or .243 Winchester can have higher ballistic coefficients and the same or greater velocities. Therefore they are much easier to hit targets with at longer distances. The 6.5 Creedmoor (CM) bullets typically have higher BCs and are a favorite with F-class (long range precision) shooters for that reason.
My precision rifle pictured at left is a sporterized and accurized M96 Swedish rifle chambered in 6.5×55. It is best suited for 500 yards and beyond. For inside of 500 yards, I will use a .30-06 with maximum pressure loadings. The .270 Winchester would be optimal as the recoil would be much lower. Yet because .30-06 is the third most popular cartridge today and because components from the second most popular American deer rifle cartridges (.308 Winchester and 7.62 NATO) can be used for handloading .30-06, it is therefore a more practical choice.
An Aside: The last thing you want to occur is running out of ammo. Many battles are lost because one of the participants ran out of ammo or water. One of the biggest reasons attackers lose is because they have to bring their supplies in on their backs which includes food… It has often been quoted: “Armies travel on their stomachs”. (Napoleon Bonaparte.) Their weakest link is their logistics train. Logistics win wars.
Rifle Bullet Trajectories
The combination of ballistic coefficients and higher and lower velocities determine the trajectory and the ability to buck the wind. Always choose the ammunition with the projectile with the higher ballistic coefficient for long-range target shooting. For ranges under 300 yards, flat-based bullets will often be more accurate in many rifles, but boat tail bullets become more accurate as they stabilize out past 300 yards and slip through the air and buck the wind with much greater efficiency than flat-based bullets.
For a long-range application always choose the ammunition that comes with bullets that have the higher ballistic coefficient. Hornady’s ELD line of cartridges are worth the higher price as these are an excellent choice for long-range shooting. But if these are too spendy for your budget, choose ammunition that uses a boat tail bullet and compare the ballistic coefficient with several different boxes of ammunition. Buy the one with the highest ballistic coefficient that will have a value greater than the other. For example, a typical .223 55-grain FMJBT bullet will have a B.C. of 0.243 and a 75 grain boat tail that is a open tipped match (OTM) bullet or polymer tip bullet might have a B.C. of 0.395. That is nearly the same as a .308 150-grain FMJBT. The 6.5CM 140 grain boat tail bullets that are best suited for long-range target shooting can have a ballistic coefficient in the neighborhood of 0.580 or greater. This 6.5 CM bullet has a BC similar to that of a 190-grain to 200-grain boat tail .308 bullet.
This is information that the manufacturer provides on the box, or it can be found online. If the ammunition does not shoot as accurately as a flat-based bullet in your rifle, if it close is fairly close in size, then I would still choose the ammunition that advertises the bullet with the highest ballistic coefficient. As the boat tail bullet gets beyond 300 yards it should settle down and fly straighter and become more accurate at greater distances and it will buck the wind much better. Thus, the shooter does not have to work as hard to compensate for wind drift. In summary: A bullet with a high ballistic coefficient will fly much flatter, buck the wind much better, and retain its energy much longer.
Putting It All Together
Federal produces ammunition that can typically shoot Minute of Angle (MOA) groups. These are groups about 1 inch in diameter ayt 100 yards — at least in rifles that are so capable. Hornady and Federal would be some of the first brands to test. Lower-cost Privi Partizan brand ammunition offers low-cost match-grade ammunition using FJMBT. This might work as well. To find commercial ammunition that will shoot well in your rifle, I recommend shooting 10-round groups. Let the barrel cool down between shots and shoot the next ammunition to be tested in the same space of time used to shoot the first group and so on.
Modern ammunition and modern rifles are typically more accurate straight out of the box than they were 20 years ago, because they have figured out how to test for bullet concentricity and tighten up variances in production lines. This makes more an accurate rifle affordable with modern manufacturing methods and materials. Decades ago it was hard to get a MOA rifle out of the box, but now it is commonplace. To wit, Savage and Mossberg both sell entry-level models that can shoot MOA.
Setting Up A Scoped Rifle
In general, ordinary hunting rifles using commercial ammunition should shoot 2 MOA or less. This is good enough for taking 4 legged critters at ethical hunting ranges of 250 yards or less. If it does not shoot like this, then try a different type of ammo. You will need enough ammo of the same kind to practice and to shoot with so that you know how the load shoots and can have confidence in it. I would have no less than 200 rounds in reserve that the rifle shoots well with and is zeroed with. If the rifle shoots bad, then see if the scope is loose or is broken, or the screws that hold either the scope or the rifle in the stock could also be loose. Use Permetex blue-colored or medium-strength Thread-Locker on the screws that hold the scope mount in place. On precision rifles, I would also use a very thin layer of JB weld or other epoxy as a shim between the rifle barrel and bottom of the scope ring mount. It is like bedding the action to the stock. The action needs a rock-solid connection with the stock so that it can mechanically support a free-floated barrel.
For the common hunting rifle with iron sights or scope, adjust the sights or scope so that this group is in the center of the target at the point in its trajectory to where is it zeroed. There are lots of videos on this topic. Adjust the scope for a 200-yard zero. Start by bore sight zeroing the rifle at 25 yards (this is called a ‘hasty zero’) and then confirm at 100, 200, and 300 yards and then fine-tuning the scope, accordingly. You may wish to shoot at this distance to make sure you and the rifle and bullet can hit at that range with enough accuracy to be useful. I can do 200 yards offhand with iron sights with M193 ammunition without practicing, but a scope is far better and easier to hit with. A scope is necessary to locate and identify the target that is hiding.
A 200-yard zero is also good for hunting out to 250 yards. If you need to shoot at 300 yards, simply hold a tad high. Refer to the JMB chart to see what a “tad high” means, about 8 to 10 inches, or at about shoulder height, or less if you are shooting a cartridge that has a flatter trajectory such as .243 and .270 Winchester, and full power 150-grain bullets out a .30-06 or .308 Winchester. To get the most out of these cartridges a traditional battlefield zero at 300 yards is more appropriate if your hunting scope has enough travel to by zero at 300 yards. With flat-shooting cartridges with a 300-yard zero, it would be possible to hit as far out as 475 yards by aiming at the top of the head.
The Arken SH-4 Gen 2 scope has more than enough ability to adjust, about 110 MOA. If you cannot afford this low-cost scope, or would rather use your Leopold, install a Picatinny rail scope mount with 20 MOA elevation built into the scope mount. This will make adjustments beyond 500 yards possible using a scope with a 1-inch tube.
Wind deflection will be a significant factor out at 300 yards as the bullet will be pushed left or right 5 to 10 inches in a 5 to 10 mph full-value crosswind. I round off numbers so that they will better stick in my memory. Sometimes is it better to be accurate rather than precise.
In tomorrow’s final installment of this article, I’ve included a basic ballistics chart for 5.56 NATO, 7.62 NATO and examples of flat shooting cartridges like .308 Winchester that you can study. Longer-range cartridges use lower velocities and bullets with very high ballistic coefficients to hit well out at 500 to 1,200 yards and beyond.
7.62 NATO M80 is a battlefield superiority cartridge given its performance, cost, and availability. But there are better cartridges if you can afford to stockpile enough ammunition. I roll my own. If you need to shoot out to 400 yards using M80 ball or 5.56NATO, then aim at the top of the head and the bullet will strike about 2 feet lower — just below the belt line. This is what is referred to as battlefield accuracy that is not at the level of accuracy needed to ethically take big game.
(To be concluded tomorrow, in Part 4.)