Wasn't feasible. The .45 is an excellent weapon, but for military applications, the ability to carry more rounds far outweighs any advantage in stopping power the .45 has.
My Glock 30 carries 10 with one in the pipe and its a small gun. Strap on a pair of extra magazines and you've got 28 rounds (9 X 3 plus one in the pipe) ready for action.