Miller is quite correct, and Major Sir Gerald Burrard in the second edition of The Modern Shotgun (1948), Volume 3, The Gun and The Cartridge, The Diagnosis of a Burst discussed Wave Pressures and the etiology of multiple bulges pp. 364-375. The second looooong bulge starts about 1 1/2" past the end of the first, and is shown quite clearly on the full size radiograph.

Monty - the right barrel was .090" at 4 1/2"