Wat no.
It's the caliber that's important (and powder load, and materials used in the bullet and chamber, but whatever), not what you call the rifle.
That said, the M14 is a 150 gr, 7.62x51 mm cartridge, whereas the AK-47 is a 123 gr, 7.62x39 cartridge. Important to remember that grains (gr) is the weight of the entire bullet and cartridge, not the amount of powder in the cartridge.
That said, the M14 will indeed outperform the AK-47 against kevlar.
EDIT: It's called a 'battle rifle' instead of an assault rifle because assault rifles by definition have to be selective fire. The M14 is exclusively semi-automatic, unless you mess around with the feed mechanism.