It is made to pen ERA, many get this wrong as they think the m829a3 gets way more penetration like upwards of 750-900mm but that is wrong.
The m829a3 actually (if estimated correctly) gets very small benefits when it comes to penetrating power compared to the m829a2, However the M829A3 is equipped with a solid steel tip (~100–152 mm long, with a engineered weak joint) which sacrifices itself against ERA so the rest of the sabot/penetrator can go cleanly through the armour.
The m829a2 was built on the emphasis of “raw power” while the m829a3 takes on armour in a more elegant way/smart way
Kinetic Energy comparison:

→ Almost identical total energy. The extra 1 kg mass in the A3 perfectly offsets the ~120 m/s lower velocity.
Bending Stiffness (the real anti-ERA advantage):

• A2 diameter ≈ 22 mm
• A3 diameter = 25 mm
• Ratio: (25/22)^4 \approx 1.67 → +67% bending stiffness
This is why the steel tip works: it detonates the ERA plates early, the weak joint shears it off, and the thicker main DU rod resists guillotining/bending far better than a monoblock rod.
Proof It Was Designed to Penetrate Relikt-Level ERA
Wikipedia (sourced from U.S. Army/ATK data):
“The M829A3 is a further improvement, designed to defeat any future armor protection methods like the newer Kaktus type, which was fitted on prototype tanks such as the Black Eagle tank, later developed into Relikt (ERA).”
The steel tip detonates the ERA early; the main DU rod finishes the job. Diameter increase gives 67% more resistance to bursting plates.
Below The Turret Ring / ATK patents:
“Such a penetrator design has a big benefit against targets protected by heavy ERA, which is what the main target of the M829A3 development was.” → +20–30% effective penetration vs heavy ERA arrays (Kontakt-5 or follow-on like Relikt).
Real-world mechanism (confirmed in every patent and analysis):
The tip acts like a mini-tandem charge against ERA. It triggers the explosive before the main rod arrives, so Relikt’s flyer plates only hit the sacrificial steel instead of deforming the sharp DU point. Without the tip, the A2 loses 20–30% penetration from tip blunting/guillotining. With the tip + thicker rod, the A3 retains far more residual performance.
A picture so it’s easier to visualize the steel tip against era

And link to that video https://youtu.be/QKHhrZQHs2E?is=SMGilAUJrWV68A2h