Currently, the typical law enforcement patrol rifle is a semi-auto M4 carbine. A few agencies go with the military 14.5-inch barrel, but most choose the 16-inch version. The choice of the M4 carbine offers various advantages. The adjustable stock allows the carbine to be readily usable by officers of varying sizes. Current M4s allow the ready mounting of an optical sight to aid in accuracy, such as a red dot sight of some type. For typical urban/suburban situations, the 5.56 round gives enough range, penetration, and striking power to give the officer an advantage over the pistol. There is also a certain intimidation value in getting out of a patrol car with a carbine. To be honest, I’m old school enough that I think the intimidation factor is as great or greater with a Remington 870 riot gun, but lately shotguns are out and carbines are in. Another factor that has recently weighed in favor of the M4 carbine is the large number of law enforcement recruits who have military experience and are therefore very familiar with the M4 platform.
A Case For More Power
Now that M4-type carbines are available chambered for the 7.62x51mm NATO round, there are some military and law enforcement personnel who feel they’d rather be armed with a weapon chambering the more potent round. The 7.62x51mm gives more range, penetration, and striking power. Yes, the 5.56x45mm M4 is normally lighter and handier, but as more accessories have been added to the M4 it has gotten heavier itself.
Generally, the patrol carbine’s mission is seen as urban countersniper deployment, elimination of rabid animals, and engaging criminals armed with rifles or carbines or at a distance. Agencies with M4s or other carbines also normally train to use them in active shooter situations. The 5.56 M4 will normally perform these missions quite well.
Some law enforcement missions, however, could be performed more effectively with a 7.62x51mm carbine. For example, fish and game agents who might have to put down large animals or deal with illegal drug growers or other criminals armed with rifles or shotguns, possibly at some distance, would find a 7.62x51mm carbine very useful. In fact, instead of carrying a large caliber bolt-action rifle and a 5.56 M4 in their vehicles, one 7.62 carbine could perform multiple functions. The 7.62x51mm carbine is also more effective in the countersniper role. Certainly, to 500 yards or more a 7.62x51mm M4-type carbine with good optics could reach a shooter, punch through barriers, and put him down. And, in areas where winds can go fairly high, the heavier bullet offers a much better chance of hitting the target at distances. Remember, the average user of a patrol rifle will not be trained to dope a shot to the extent that a sniper will.
Because of the number of cases where law enforcement officers encounter criminals, especially active shooters, wearing body armor, some consideration should be given to availability of a round capable of penetrating body armor if a shooter has Level IV body armor that will protect against a hit from even 7.62x51mm NATO Armor Piercing ammo (US M2 AP). Level III body armor will protect against FMJ (US M80) 7.62x51mm NATO. Those same two levels offer protection against 5.56x45mm NATO M855 ammo. Generally, however, at longer distances, a 7.62x51mm round will be more effective against a subject wearing body armor than a 5.56x45mm round. Multiple hits with a 7.62 AP round, even on Level IV armor are more likely to put the subject down. Good optical sights should also allow placement of shots into the head or legs.
I could see an argument, too, for arming certain officers who have military training or who show strong marksmanship abilities with the heavier carbine even if other members of the agency are armed with 5.56 carbines. The officers with the 7.62 carbines could function much as military designated marksmen when needed. If the 7.62 carbine is of M4-type, then the typical bureaucratic argument that officers will get confused doesn’t apply as the system is the same. Or, there is another option—officers who could function as “designated marksmen” could be armed with the Colt 901 Modular Carbine, which allows the rifle to be quickly converted between 5.56 and 7.62 calibers. For normal duty, the 5.56 upper could be used, but in counter-sniper or other situations requiring a more powerful carbine, it could be quickly switched to 7.62x51mm caliber.