I asked my father this very question a few years before we lost him to cancer at age 80.
He said that during his four months in theater roaming through France and Belgium (and trying to cross the Rhine river as the Germans defensively shelled and mortared his buddies and him), he got the opportunity to carry just about everything. BAR, Reising submachine gun, M1 Garand, Thompson, and M1 carbine for example.
He said that whenever he carried and used anything that was full-auto, he felt like he "had a big target painted on" him. He didn't like to talk about the war much, but I gathered that a good portion of his time was spent doing the same street fighting that was in the movie "Band of Brothers." It was during this combat that everytime he fired a burst of full-auto, the Germans would decide that he was worthy of their intense attention.
All of these weapons were heavy, and even though he was a strapping 6-foot-something and 220 pounds (and I later learned -- a full football scholarship to U of Pitt prior to being drafted), he preferred the light weight of the M1 carbine and as much ammo as he could carry. Kind of surprised me a bit.
The week of his funeral, we went through his momentos. That's where I found the letter from U-Pitt. Turns out that although he got a full ride, this son of a barber in a coal mining town couldn't afford the cost of books.
I knew that he was awarded a Purple Heart for severe injuries he suffered near the Rhine in a mortar barrage (left for dead in the mud with shrapnel through his lung, but was able to raise his hand to signal the last retreating jeep). This happened in or around the Ardennes just two weeks before the Battle of the Bulge. Next surprise... in his four short months, he was awarded not one, but four Bronze Stars. He never told us about them.
Hmmm. M1 Carbine. I just have to get one.
Rick