The Great Halftrack Debate 428!

[RedDevil]

Early vehicles had a pintle mount just behind the front seats mounting a .50 caliber (12.7 mm) M2 Browning machine gun. The later M3A1 adopted a raised, armored 'pulpit mount' for the .50 caliber, and .30 caliber (7.62 mm) machine guns could be used from mounts along the sides of the passenger compartment. Many M3s were later modified to the M3A1 standard.

http://en.wikipedia.org/wiki/M3_Half-track


So case in point YES the .30s could be unmounted and used in a ground supporting role. The .50 however is a huge HEAVY beast and without a tripod base, I would say it was NOT used in the manner that you're inquiring about.