Quoted:
I don't think there is any question that .308 FMJ will penetrate far more than 5.56 FMJ.
5.56 ap 'might' penetrate more than 7.62 FMJ, but I highly doubt it.
and........you would be wrong....
PERFORMANCE OF TYPICAL MILITARY RIFLES AGAINST
NATO 3.5mm STEEL TEST PLATE
AKM 7.62x39mm PS: 300 CP, 400 50% CP/50% PP
AK-74 5.45x39mm PS: 600 CP, 800 FP
M16A1 5.56 M193: 400 CP, 500 50% CP/50% PP, 600 FP
M16A2 5.56 M855: 600 CP, 700 CP, 800 50% CP/50% PP, 1000 FP
Rifle M1, Ball M2: 500 CP, 600 FP
Rifle M14, Ball M80: 700 CP, 800 FP
Rifle M21, M118 Special Ball: 800 CP, 900 50% CP/50% PP, 1000 FP
Carbine M1, Ball M1: 100 CP, 200 FP
CP= Complete Perforation in which a major portion of the projectile exits
the armor. PP= Partial Penetration in which a hole is generated but the
major portion of the projectile does not exit the armor. FP= Failure to
to Penetrate, the plate may be dented but it is intact.
This data is from testing conducted by the USMC Firepower Division
at Quantico, VA during the Modified Operation Test in the early 1980's.
Keep in mind bullet construction has a lot to do with penetration. The 7.62mm M80 ball
load is an old design from the 1950s with a simple lead core. The M855 has a mild steel
core and is smaller in diameter and does better against steel. However, change the
barrier type and the M80 ball load might do better.