Optimizing Self-Defense Ammunition for a Short Barreled AR Pistol

The choice of ammunition for self-defense in a short-barreled AR pistol is critical for ensuring both effectiveness and safety. With a 10.5-inch barrel, it's important to understand the dynamics of the ammunition and how it impacts performance.

Understanding the Basics

The 5.56mm system relies heavily on the velocity of the bullet for its effectiveness. In the past, M193 ball ammo with a 55gr FMJ bullet was commonly used. While it worked well at close range, its performance dropped significantly at longer distances.

Today, advancements have been made with the 62gr bullet, which offers improved performance at higher velocities. However, in case of doubt, hollow point loads can be an excellent alternative. Hollow points are less likely to penetrate and inflict more damage, making them a safer option.

Close-Range Effectiveness

At close range, the 55gr FMJ M193 ammo performed reasonably well due to its high velocity. However, as range increases, the effectiveness drops dramatically. The 5.56mm rounds depend on velocity for their damage potential. At closer distances, high velocity translates into better penetration and fragment distribution, but at longer ranges, it falls short.

Two Key Options

There are two primary routes when choosing ammunition for self-defense: lighter, fast frangible ammunition and heavier ammunition.

Frangible ammunition relies on physical deformation and fragmenting to impart damage. The 55gr FMJ M193 ammo, which is similar to the 55gr FMJ .223 Remington out of a 10″ barrel, starts at the minimum velocity required for reliable fragmentation, around 2600–2700 fps. This works well indoors but not over long distances.

On the other hand, the 77gr "Razor Core" is a military copy of the Mk.262 loading, which is less dependent on velocity for fragmentation. This makes it a more reliable choice, especially if you have the budget for it.

Heavier Bullet Recommendations

For optimal performance, a heavier bullet is recommended. Ideally, a longer barrel with a 62gr bullet would be ideal for most shooting needs. A shorter barrel doesn't always provide the advantages it seems to have. Instead of a short-barreled AR pistol, consider a bullpup rifle where the longer barrel is set back. This results in a shorter overall firearm with a much more efficient length rifle barrel.

Comparing Ammunition Performance

With a 10.5-inch barrel, you are slightly over 2500 fps compared to 3000 fps out of a 16.5-inch barrel. Therefore, the performance difference between FMJ and JHP (expanding) ammunition is minor unless you hit center mass, which is highly unlikely in a self-defense scenario. Even then, you run the risk of a pass-through, potentially hitting a bystander.

My recommendation is to consider where you need reliable self-defense ammo for a rifle. For instance, a Sig P320 Compact with 124gr Federal HSTs would be a better choice, unless you are facing a bear, in which case 5.56mm would be foolish. In such a situation, a lever action in .45–70 would be more appropriate, but that's just my personal preference.