Lumper;
Modern body armor is rated as to the highest level of threat it can defeat- IIA is what most concealabloe BA is rated at- stops 9mm at 1200fps etc ( NIJ certification -google it).
IIIA is what most external BA begins at- heavier, bulkier but certainly more effective- rank and file troopers wear IIIA or IV plus small arms plates (SAPI ceramic matrix) rated at 308 AP capability.
The venerable and often encountered 762x 39 round is rated above IIA but well below SAPI, so it is defeated quite a bit on both the Kevlar IIIA/IV and definitely on SAPI plates based on range and other dynamic factors.
The 762x39 round from an AK is leaving a 16inch barel at not much over 2300 fps, so it has much less ability than 556 x 45 NATO ball ( 762x39 has less velocity and greater frontal area, but more mass) to defeat Kevlar or similar BA.
I have not m=been hit by a rifle round, but fragments and debris are often not felt, but a solid hit from a round on either soft or plate armor can knock the wind out of you/push you around, but remember, the impact of a rifle bullet is akin to getting hit with a fast pitched baseball, and most of us don’t wind up on our butts if hit in the torso by one n baseball. The neurologic effect is much more apparent than the physical effect if the round is defeated.
More updated BA is used at tier one levels ( SF/SEAL Ranger Force Recon etc).
Thanks. I agree with the effect of a 7.62 mm round. I damn sure do not want a 5.56 mm muscle group wound. The BA was a wise investment. Again thanks.