For the past two nights, I've covered how to zero your rifle, as well as proper shot placement. Tonight, I'll cover a subject that is every bit as important and often overlooked even by experienced hunters.
I'm talking, of course, about ammunition selection. Remember when we discussed ammo types during the lesson about ballistics tables and zeroing your rifle? Well, the type and weight of ammunition a person should select is dependent upon three things...and must, as we learned earlier, be determined prior to zeroing the rifle properly.
By this point, you likely know that the term "rifle" comes from the grooves cut into your barrel that cause the projectile to spin as it flies downrange. This spinning acts as sort of a "gyroscope" effect, stabilizing the bullet more than a smooth-bore musket would. This is one of the reasons why those who hunt with shotgun slugs will often swap out a smooth-bore barrel for a slug-specific rifled barrel.
The "twist rate" of a barrel refers to the length a spiralled rifling groove must travel down the barrel before it makes a 360 degree twist. A 1:10 twist rate will provide one revolution of twist in ten inches of barrel. A 1:7 twist rate is said to be "faster", as it provides one revolution in only seven inches, while a 1:12 twist is said to be "slower" for the same reason.
Certain twist rates are appropriate for specific bullet weights. For instance, take a .223 rifle. "Varmint" rounds, used for killing small game and nuisance animals such as gophers, are typically found in the 40-45gr range, and used with slower twist rates. The standard military-issue infantry round (albeit in a 5.56 chambering, it's essentially the same cartridge for purposes of this discussion) is a 62gr round and is used with a 1:7 twist barrel.
While the 40gr round can be used with a 1:7 barrel, and the 62gr round can be used with a 1:12 barrel, the faster twist of the 1:7 has actually been shown to cause some light-weight rounds to disintegrate mid-flight due to centrifugal force. On the other side of the equation, a slower twist rate such as 1:12 will cause the heavier round to destabilize in mid-flight, and will cause the round to actually tumble end over end resulting in what is known as a "keyhole" (impacting on its side, rather than tip, causing an elongated entry).
Even if your round does not fly apart or start tumbling, an improper twist rate for a given bullet weight will cause issues with accuracy.
For the purposes of this discussion, let's take my HK91 and compare it to my Springfield M1A Super Match. Both are civilian-legal semi-auto variants of their respective select-fire military counterparts, and both are chambered in .308 Winchester/7.62x51 NATO (there are slight differences in case wall, but largely irrelevant with either rifle, as both are civilian models).
The German has a 1:11 twist rate just like its' military brethren, intended for use with the standardized 7.62x51 NATO 147gr FMJ ammunition. The Springfield, on the other hand, has a "match" barrel with a 1:10 twist designed for 168gr rounds. Using either round in either rifle is acceptable from a safety standpoint, and both will provide decent accuracy.
With the proper ammo, however, shooting the HK off a bench will put three rounds into a quarter at 100yds. The Springfield will put them into the same hole. Needless to say, proper bullet weight is everything, and you need to know your twist rate before you can determine your proper bullet weight. After you determine your proper bullet weight, you can then move on to step 2.
After determining proper bullet weight, you must next look at the actual design of the bullet. With the exception of an extremely small selection of purpose-built rounds for the military, bullet types are typically relegated to Full Metal Jacket ("FMJ"), Jacketed Hollowpoint ("JHP"), Pointed Soft Point ("PSP"), and Ballistic Tip ("BT").
FMJ rounds will provide the greatest degree of penetration, but the least degree of bullet expansion/deformation. JPH rounds provide less penetration than the FMJ round, but more expansion than FMJ and more accuracy than PSP. PSP rounds offer a greater degree of expansion, but sacrifice accuracy and velocity due to the oft-blunted soft tip that is typically deformed prior to even being taken out of the box.
Ballistic-tip rounds, such as the Hornady A-Max and Winchester Ballistic Silvertip, are boutique hunting rounds that use a hollowpoint bullet whose tip has been filled with a pointed section of ballistic nylon or other plastic. While the plastic tip does not necessarily aid in expansion of the bullet, it does aid in aerodynamics, which provides greater accuracy and velocity than a same-weight JHP. The biggest downside to the ballistic tip round, of course, is that it typically costs $30-50/box of 20 rounds.
The biggest determining factor for you and your rifle is "how much is enough"?
Are you a hunter who feels most comfortable taking torso shots? Do you use a large-caliber rifle? Are you an experienced marksman and hunter that feels comfortable knowing that you can put a round up a flea's ass at 500yds?
John Taylor, experienced African safari hunter, developed what is known as the "Taylor KO" index. It calculates bullet weight, bullet diameter, and velocity to provide a "Knock Out Factor". A .454 Casull (for a long time, the largest standard-production handgun caliber available) gets a KO of 30, while a .22LR round gets a KO of 1. By comparison, the 5.56mm NATO 62gr round used by the M16/M4 rifles of our military get a KO of 5, while the 7.62mm NATO 147gr round gets a KO of 19.
The higher KO factor of your round, the less reliant you are upon expansion. Expansion, of course, is what creates a larger channel of wound or bodily destruction. The higher your KO factor, the more hydrostatic shock you will produce. Hydrostatic shock is caused by sudden blunt force trauma upon liquid-filled tissues found within a mammalian body. Essentially, it's the impact shoving your blood and other bodily fluids elsewhere at such a high rate of speed that the movement of fluid in and of itself causes damage. "The bigger the thump, the bigger the pump".
A light-weight .223 PSP round may expand to the same diameter as a .308 FMJ round, thus creating essentially the same wound channel. Now let's look at the difference. A baseball weighs about five ounces. Imagine Nolan Ryan just hit you in the chest with a 5oz lead fishing weight...weighs about the same as a baseball. Now imagine that you got hit in the chest with a 15oz steel hammer, roughly the same diameter, at the same speed. Harder material, and a lot heavier. The fishing weight is going to knock you down. The hammer is going to knock you out of your boots.
Is bigger better? Not necessarily. If the round is so big that it's overkill, there's no point in it...it's going to be big, expensive, and good for nothing more than showing everyone that you're compensating for your small penis. On the other end, the .223 round is so small and light that many states have outlawed its use, forgetting the fact that the same round used to hunt 170lb deer is also used all over the world to kill 170lb men.
My first deer kill was with a 55gr .223 Winchester Ballistic Silvertip, shot placement put the animal out of its misery before the muzzle blast faded. I had good shot placement, and all went well.
If you look closely, you can see the entry wound a few inches below the ear. The deer had its head down while feeding, and was shot from 80yds. While the round disintegrated upon impact, fragments did exit the top of the head, slightly visible in the photo. Good shot placement and a lot of luck killed that deer. I still prefer headshots on the grounds that they don't spoil meat, but my next kill will be with a heavier round. As my uncle says, "I've tried everything...but I just can't make those horns taste good!". A heavier round will do a better job of covering my ass in case the deer flinches, I jerk my shot, or anything else that puts me slightly off-target. If it happens to blow off one of its horns, I'm not that concerned! For the "trophy hunter", using a heavier round against the vital organs has its obvious benefits.
What round is best for you? Well, that's something you're gonna have to figure out for yourself. Every rifle is different, even rifles that are made to the same exact specs. You'll have to experiment. That's why we do this in the off-season. We figure out what works best, and we use it.
A good start to this is to determine the twist rate on your rifle, and then make use of the interwebz to find professional recommendations as to what weights are best for it. Look for online reviews of your rifle by well-known gun magazines.
Once you've figured out what weight works best for your rifle, figure out what round works for you, through trial and error. In this day and age, modern manufacturing techniques should allow for 2moa accuracy using any off-the-rack rifle when used with appropriate ammo. That's 2" grouping at 100yds. When properly zeroed, that's within 1" of your target in any direction. Experiment with different types, different brands, etc.
One of my biggest recommendations is that you should not equate price with accuracy when it comes to ammo. Obviously, with a firearm, a $1,000 rifle is going to typically shoot better than a $200 rifle. The same cannot be said with ammo.
To give an idea of what's happening here, let's look at the target above. It was posted at a standard 100yd range. The green dots were fired at "center mass", using 55gr PSP. As you see, there's a pattern of several inches. Those are standard name-brand "hunting" rounds. The blue dots are USA-made Federal 55gr FMJ rounds, and they span a pattern of a little over one inch. The red dots are the cheapest brass-case Monarch-brand ammo my local Academy had to offer, manufactured in Serbia by the Prvi-Partisan.
As you can see, a particular brand of ammo plays as much of a part in your selection as the type.
Practice and experiment, and remember what your Little League coaches taught you. You're gonna play how you practice!