Adobe Walls by Robert Vaughan
The Civil War is finally over, but when Major Hank Dawson returns home to Mississippi, he finds all his loved ones dead. Hank wanders West, until he stumbles on the town of Adobe Walls. Soon the town comes under attack by nearly 400 bloodthirsty Cheyenne. Outnumbered and desperately low on ammunition, the town's only chance for survival rests on Hank's shoulders. It's vengeance time.