Ball Ammo

Ball ammo, also known as FMJ ammunition (Full Metal Jacket), is the standard military-style cartridge featuring a lead core bullet encased in a harder metal jacket, typically copper or copper alloy. The term “ball” originated from early military nomenclature when round musket balls transitioned to conical projectiles, with the military continuing to use “ball” to designate standard service ammunition.

What Is Ball Ammo?

Ball ammo FMJ ammunition consists of a lead core completely surrounded by a metal jacket, creating a uniform projectile that maintains its shape during flight and impact. In 5.56x45mm NATO, the most common ball ammunition is M855 (62-grain with steel penetrator) and M193 (55-grain), while 9mm ball typically comes in 115-grain or 124-grain configurations.

Why It Matters for AR-15 Builders

When configuring your build on the AR15 Outfitters builder, understanding ammunition compatibility directly affects several component choices:

• Barrel twist rate: 1:7 twist stabilizes heavier bullets like 62-grain M855, while 1:9 works best with lighter 55-grain M193
• Gas system tuning: Military ball ammo typically generates consistent pressures, making it ideal for initial gas system setup
• Magazine selection: Some magazines feed ball ammo more reliably than hollow point alternatives

Practical Considerations

Ball ammo offers several advantages for AR-15 shooters. The FMJ bullet design provides reliable feeding in semi-automatic firearms, typically costs 20-40% less than hollow point alternatives, and delivers consistent muzzle velocity for predictable trajectory. Most indoor ranges require FMJ ammo due to reduced lead exposure and backstop wear.

However, ball ammunition penetrates more than expanding bullets, making it less suitable for home defense where overpenetration poses risks. For hunting applications, many states prohibit FMJ ammunition as it lacks the expansion necessary for ethical game harvesting.