I can attest that there are some huge rattlesnakes in N. Louisiana. My father (a logger when he was young) and I were looking over some inherited property near Eros, LA about 20 years ago when we came across two of the largest rattlesnakes either of us had ever seen. He killed them both with a hoe after dragging them out of a stump hole.
My dad is 6'-5" and lifted the larger dead snake above his head (arms fully extended) and the end of the snake still had about a foot in length remaining on the ground. The head of the snake was as big as his fist. We were convinced that no man could have survived a bite from either of these enormous snakes.