The rifle has some major advantages over the pistol or shotgun when used as a defensive firearm. The rifle is far more powerful than a pistol and offers a quicker reload than the shotgun. With standard magazines holding 20 or 30 rounds, the rifle offers a capacity advantage as well (I have some 33 rounders for my Glock, but those are the exception, not the rule). As a shoulder fired firearm, the rifle’s practical accuracy in rapid fire trumps the pistol, and its relative lack of recoil allows for faster follow-up shots than the mighty 12-gauge shotgun. The rifle can be fired more quickly and more accurately than any other defensive choice available.
However, one of the big advantages of using a centerfire rifle cartridge for self-defense brings a serious concern along with it. The rifle’s ability to stop bad guys, penetrate barriers, and defeat “soft” body armor becomes a double-edged sword when the legal liability of over-penetration is considered. Fortunately for civilians using the rifle as a defensive arm, a wide variety of ammunition choices are available, especially in the very common .223 Remington and 5.56 NATO calibers. At this point, I should mention that these two calibers are NOT the same even though their external dimensions are very similar. Rifles built to withstand the significantly increased chamber pressure of 5.56 NATO can also shoot .223 Remington ammo without difficulty, but the reverse is not always true. Know your firearm and use the proper ammunition for it.
Likely the worst choice for defensive ammo is the inexpensive Russian-made, steel-cased full-metal jacket stuff that we have all used as practice ammo at one time or another. It’s affordable, and I have converted thousands of rounds of it into smoke and noise over the years. However, its full metal jacket bullet is a simple pointed nose design with a thick copper jacket around its lead core, which will not expand or fragment when it hits the muscle and bone of the bad guy. These bullets tend to travel straight through whatever they hit and keep going for quite awhile afterward before eventually tumbling. Remember, if the bad guy dies from blood loss in a hospital hours later, it doesn’t matter—we are shooting to stop his aggression right now! This ammo offers minimal stopping power combined with maximum legal risk. We must plan being legally liable for everything struck by the bullets we fire. A bullet which drills a .223 caliber hole straight through the bad guy before blowing through the wall behind him is the worst combination possible.
A slightly better option, while still being crippled by the full metal jacket bullet design, is the 5.56 NATO military specification M193 round. The 55-grain bullet is similar in outward appearance to other FMJ rounds, but features a thinner copper jacket around the lead core. When the bullet hits with sufficient velocity (greater than 2,600 feet per second or so), the extreme pressure of striking the target is sometimes too much for the thin jacketing to keep the bullet together. If the jacketing breaks at the cannelure (the groove around the bullet where the casing crimps to hold it), the bullet will fragment into several smaller chunks which spread out in all directions. They are unlikely to pass all the way through the bad guy’s body with enough force to do damage to anything else behind him. A 5.56 NATO round which fragments inside the chest cavity of a bad guy is very likely to stop him right there. Unfortunately, the fragmentation of the M193 round is not a consistent sure thing at all; even under strict testing conditions, only a certain percentage of rounds will do it. There is no evidence that the military wanted a fragmenting bullet design or was even aware that it could fragment when they adopted the M193 bullet way back in 1964. The fact that it does sometimes fragment is really an accident of bullet construction techniques rather than the feature for which it is now known.
The other military specification round, the 62 grain M855 (USA) or SS109 (NATO) loading, can also fragment like the M193 does, but it doesn’t fragment as often or as violently as M193. The bullet design of the M855 is complicated, featuring a full metal jacketing over the pointed lead bullet and a steel penetrator core at the bottom. It is slightly heavier than M193 but offers less velocity. This ammunition was designed in the 1970s specifically to penetrate one side of a Soviet steel helmet from a distance of 600 meters, which seemed like a great idea at the time. In the real world, M855 has had some disappointing results. In the 1993 Battle of Mogadishu (Blackhawk Down), Delta Force soldiers reported frustration with shooting enemies multiple times only to see them get up and run away. The combination of their short barreled (10.5-11.5 inch) CAR-15 type rifles and M855 ammunition did not produce enough velocity for the bullets to fragment; they traveled straight through the Somali fighters.
In recent years bullet technology has grown tremendously. The old soft tip hunting ammo designs have been overtaken by hollowpoints offering expansion along with good weight retention. These rounds form a mushroom shape which limits over penetration and devastates soft tissue, while holding the bullet together instead of fragmenting. Most recently, ammo makers have started capping their hollowpoints with a plastic ballistic tip. When the bullet strikes the target, the plastic tip is driven backwards inside the hollow of the bullet, helping the bullet expand reliably and more consistently. Ballistic tip ammunition offers a good mix of penetration combined with reliable expansion and weight retention. Though sold for years as hunting ammunition, manufacturers have also begun to offer ballistic tip loadings specifically for law enforcement or personal defense. For most common defensive applications, this is the pinnacle of bullet technology at this time.
Inexpensive steel cased ammo intended for plinking and training is a poor choice for use when lives are on the line. Military specification loadings are better, but their performance is inconsistent compared to the latest generation of ballistic tip hollowpoints. When loading a rifle for defending your life, choose your ammunition carefully.