There is quite alot of misinformation regarding the difference in penetrating power between old and new models of armor piercing rounds. In the former, we have the M2 AP (30-06 caliber). In the latter, we have the M995 AP (5.56x45mm caliber) and M993 AP (7.62x51mm caliber). On military forums, the popular opinion is that the M995 AP can outperform the M2 AP. Such a view is at odds with a test done 2 years ago by Brass Fetchers. The film makers fired M2 AP rounds against a 12.7mm thick plate of MIL–A 12560 steel. While the exact hardness of this alloy is unknown, its suspected to be in the region of 381-442 brinell! Another source puts it at a more conservative 390 brinell. Striking at a velocity of just 793 mt/s, the M2 AP round succeeded in penetrating the MIL–A 12560 plate.
Brass Fetchers793 mt/s is about the velocity that an M2 AP would have at 100 meters. With that in mind, we can compare its score to the M995 and M993 rounds. According to nammo, the M995 AP can pierce 12mm of steel at 100 meters, while the M993 AP can pierce 18mm of steel at 100 meters. Both of these plates are of 300 brinell hardness, which compares poorly to the 381-442 brinell plates the M2 AP was fired against. Given that even a small difference in plate hardness (as small as 50 brinell) can have a significant influence in whether or not a round penetrates, this should speak volumes about the power of a 30-06. Even without a tungsten core, it is superior to the M995, and not far behind the M993.  The fact that ceramic armors can withstand even one shot from these projectiles is impressive.
This was a test done 4 years ago by On Target Tactical. It involved a government-issue level IV plate (supposedly an ESAPI) being shot three times by an M1 garand from 10 yards. This is in accordance with military testing standards, and with the contract description for ESAPI.  But instead of the 168 grain M2 AP rounds that are typically used in level IV tests, the analysts used remington 165 grain core-lokt rounds. This is a soft point bullet with less penetrating power than an FMJ, never mind armor piercing. Of the three rounds fired at the ESAPI plate, one made a full penetration, which is a fairly shocking result. This test seemingly confirms the ESAPIs poor tolerance for multiple hits, especially if they strike in a tight grouping.
On Target TacticalSome critics have attempted to claim that the plate was inserted backwards into the vest, but this is patently false. The front of the plate shows evidence of three hits, while the back shows evidence of just one, and thats the shot that perforated through both sides. Others have pointed out that ESAPIs are not stand alone capable, and must be used in conjunction with level IIIA soft armor. This is a valid point, and its not quite clear whether the vest in question (TPC tactical plate carrier from pantac usa) has kevlar panels built into it. But since the analysts weren't even using armor piercing rounds, it wouldn't make a major difference anyways. Clearly, ESAPI plates can be defeated with a full power rifle by using a double tap.
Army plates are tested with a minimum spacing of 6 inchs.
If the rounds strike any closer together, the plate will crack
 Compared to the M995, it can penetrate the same thickness of harder steel at the same distance. Compared to the M993, it can penetrate a lesser thickness of harder steel at the same distance.
 According to wikipedia: “Military testing calls for survivability of three hits from the round marked on the plate - for standard SAPI, of a caliber up to 7.62×51mm NATO...” “Additionally, two ceramic plates may be added to the front and back of the vest, with each capable of stopping up to three hits from the round marked on the plate.”