I once read an old article where he said he especially liked the m-1 carbine as his favorite weapon, because it was magazine fed and was light weight, with his small size that would have meant a lot.
It would also appear he did not need a gun to do damage. In his bio it stated he was once indicted for attemtped murder, seems he almost beat a man to death in a fist fight, but he was cleared of the charge.
All I can say is what he told me that night. However, if you watch To Hell And Back, he always carries an M-1 Garand or Thompson. In the Anzio scenes, he says, "Hey, give me back my Thompson!"
There is this one scene just before the TD action for his Medal of Honor. He has a M-1 carbine slung over his shoulder if I recall correctly.
The M-1 carbine is not a man-killer weapon in any event. The round is too light unless it hits a vital spot while the 30-06 and .45 will do some major damage with any hit on the torso.
IMHO Audie Murphy did not need a light weapon as he was a true warrior and used the weapons that got the job done. That being the Garand, Thompson and in a pinch, the German MG-42...