If you've been to shooting ranges, you've likely encountered the enigma of green tip ammo. This ammunition, while contentious in shooting circles, is notably absent from most shooting ranges. This consistent prohibition raises questions about its origin.
The primary reason you can't use green tip ammo at many shooting ranges is its design to pierce steel. Given that numerous indoor shooting ranges employ steel to trap bullets, the potential damage from green tip ammo can be significant, leading to financial implications for the range.
What Is Green Tip Ammo
Green tip ammo's ability to penetrate steel underscores its potency. Originally designed to breach armor, its strength has made it a topic of debate for civilian use. Introduced in the 1970s and later adopted by the US military, the green-tipped design signifies its armor-piercing capability.

Over time, the bullet's ability to penetrate steel armor has raised safety concerns, especially given its potential to breach bullet-proof vests. The bullet's capability to pass through barriers like wooden walls further accentuates these concerns.
Attempts by the ATF to regulate this ammo, due to potential threats to law enforcement, have been unsuccessful, citing Second Amendment violations. Despite its potency, many indoor shooting ranges prohibit its use due to potential safety hazards and backstop damage.
Is Green Tip 5.56 Armor-Piercing?
No, Green Tip 5.56, known as M855, is not considered armor-piercing by the BATFE. Some people mistakenly think it is because it has a steel "penetrator" at its core.

Credit https://www.wideners.com
This helps it go through barriers like glass, metal, clothing, and brush effectively. But it doesn't consistently break through car glass, bricks, or modern body armor. Soldiers in Iraq found that M855 ammo didn't always go through car windshields at close range.
The newer M855A1 is armor-piercing and replaced the original M855 green tip. But the public can't buy it. This round can even damage a truck's engine from 500 yards away.
Is M855 Green Tip Ammo Legal?
Yes, it is.
Is Green Tip Better Than FMJ?
Green tip ammo has a steel core, making it more penetrative than regular FMJ 5.56 ammo. Some shooting ranges don't allow green-tip ammo because it can damage their targets more.
As far as ballistic performance goes, here is an interesting chart found on AR15.com

M193 is set to hit targets straight up to 250 meters. At this setting, the bullet stays within 4 inches of where you aim until it reaches nearly 300 meters.
On the other hand, M855 is set for 300 meters. With this setting, the bullet is within 6 inches of the target until 325 meters. When we look at their paths up to 300 meters, M855 flies about 5 inches higher than M193 at that distance.
What is Green Tip Ammo Used For?

Green tip ammo was first called SS109 in the 1970s. It was made in Belgium and won NATO's standardization trials. These trials tested the ammo's ability to penetrate steel helmets from a distance. The U.S. Military started using it in the 1980s, renaming it M855 and painting the tips green. This color helped soldiers tell it apart from the older M193 ammo. Gun makers in the U.S. started selling M855 to the public under different names. The ammo is almost the same as the military version.
The ATF's definition of armor-piercing ammo is clear:
18 USC 921(a)(17):
(B) The term “armor piercing ammunition” means—
(i) a projectile or projectile core which may be used in a handgun and which is constructed entirely (excluding the presence of traces of other substances) from one or a combination of tungsten alloys, steel, iron, brass, bronze, beryllium copper, or depleted uranium; or
(ii) a full jacketed projectile larger than .22 caliber designed and intended for use in a handgun and whose jacket has a weight of more than 25 percent of the total weight of the projectile.
M855 vs. M193
The M193 cartridge is still made and sold to civilians. It has a 55-grain bullet with a copper jacket and lead core. Its shape helps it travel farther. Some people ask which of these two types of ammo is better. M193 is good for shooting targets and hunting. M855 is better for piercing things because of its semi-steel core.