There is a great book titled The Tunnels of Cu Chi: http://www.amazon.com/The-Tunnels-Ch...d-Battlefields
It describes a wide range of weaponry including handguns, both standard and modified, in .22, .25, .38 .45 and .44. According the the book, the 1911 was too big and bulky for most tunnel rats. One tunnel rat used a paratrooper M1 carbine. Others brought in chopped-down shotguns and captured AKs to confuse the VC.
One carried a German Luger 9mm and a 4-gauge shotgun. Yes, a 4-gauge!