The rifle served adequately during its brief tour of duty in Vietnam. Though it was unwieldy in the thick brush due to its length and weight, the power of the 7.62×51mm NATO cartridge allowed it to penetrate cover quite well and reach out to extended range, developing 2,560 ft·lbf (3,463 J) of muzzle energy. However, there were several drawbacks to the M14. The traditional wood stock of the rifle had a tendency to swell and expand in the heavy moisture of the jungle, adversely affecting accuracy. Fiberglass stocks were produced to resolve this problem, but the rifle was discontinued before very many could be distributed for field use. Also, because of the M14's powerful 7.62×51mm cartridge, the weapon was deemed virtually uncontrollable in fully automatic mode, so most M14s were permanently set to semi-automatic fire only to avoid wasting ammunition in combat.